Index: node_modules/d3-quadtree/src/add.js
===================================================================
--- node_modules/d3-quadtree/src/add.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/add.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,84 @@
+export default function(d) {
+  const x = +this._x.call(null, d),
+      y = +this._y.call(null, d);
+  return add(this.cover(x, y), x, y, d);
+}
+
+function add(tree, x, y, d) {
+  if (isNaN(x) || isNaN(y)) return tree; // ignore invalid points
+
+  var parent,
+      node = tree._root,
+      leaf = {data: d},
+      x0 = tree._x0,
+      y0 = tree._y0,
+      x1 = tree._x1,
+      y1 = tree._y1,
+      xm,
+      ym,
+      xp,
+      yp,
+      right,
+      bottom,
+      i,
+      j;
+
+  // If the tree is empty, initialize the root as a leaf.
+  if (!node) return tree._root = leaf, tree;
+
+  // Find the existing leaf for the new point, or add it.
+  while (node.length) {
+    if (right = x >= (xm = (x0 + x1) / 2)) x0 = xm; else x1 = xm;
+    if (bottom = y >= (ym = (y0 + y1) / 2)) y0 = ym; else y1 = ym;
+    if (parent = node, !(node = node[i = bottom << 1 | right])) return parent[i] = leaf, tree;
+  }
+
+  // Is the new point is exactly coincident with the existing point?
+  xp = +tree._x.call(null, node.data);
+  yp = +tree._y.call(null, node.data);
+  if (x === xp && y === yp) return leaf.next = node, parent ? parent[i] = leaf : tree._root = leaf, tree;
+
+  // Otherwise, split the leaf node until the old and new point are separated.
+  do {
+    parent = parent ? parent[i] = new Array(4) : tree._root = new Array(4);
+    if (right = x >= (xm = (x0 + x1) / 2)) x0 = xm; else x1 = xm;
+    if (bottom = y >= (ym = (y0 + y1) / 2)) y0 = ym; else y1 = ym;
+  } while ((i = bottom << 1 | right) === (j = (yp >= ym) << 1 | (xp >= xm)));
+  return parent[j] = node, parent[i] = leaf, tree;
+}
+
+export function addAll(data) {
+  var d, i, n = data.length,
+      x,
+      y,
+      xz = new Array(n),
+      yz = new Array(n),
+      x0 = Infinity,
+      y0 = Infinity,
+      x1 = -Infinity,
+      y1 = -Infinity;
+
+  // Compute the points and their extent.
+  for (i = 0; i < n; ++i) {
+    if (isNaN(x = +this._x.call(null, d = data[i])) || isNaN(y = +this._y.call(null, d))) continue;
+    xz[i] = x;
+    yz[i] = y;
+    if (x < x0) x0 = x;
+    if (x > x1) x1 = x;
+    if (y < y0) y0 = y;
+    if (y > y1) y1 = y;
+  }
+
+  // If there were no (valid) points, abort.
+  if (x0 > x1 || y0 > y1) return this;
+
+  // Expand the tree to cover the new points.
+  this.cover(x0, y0).cover(x1, y1);
+
+  // Add the new points.
+  for (i = 0; i < n; ++i) {
+    add(this, xz[i], yz[i], data[i]);
+  }
+
+  return this;
+}
Index: node_modules/d3-quadtree/src/cover.js
===================================================================
--- node_modules/d3-quadtree/src/cover.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/cover.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,43 @@
+export default function(x, y) {
+  if (isNaN(x = +x) || isNaN(y = +y)) return this; // ignore invalid points
+
+  var x0 = this._x0,
+      y0 = this._y0,
+      x1 = this._x1,
+      y1 = this._y1;
+
+  // If the quadtree has no extent, initialize them.
+  // Integer extent are necessary so that if we later double the extent,
+  // the existing quadrant boundaries don’t change due to floating point error!
+  if (isNaN(x0)) {
+    x1 = (x0 = Math.floor(x)) + 1;
+    y1 = (y0 = Math.floor(y)) + 1;
+  }
+
+  // Otherwise, double repeatedly to cover.
+  else {
+    var z = x1 - x0 || 1,
+        node = this._root,
+        parent,
+        i;
+
+    while (x0 > x || x >= x1 || y0 > y || y >= y1) {
+      i = (y < y0) << 1 | (x < x0);
+      parent = new Array(4), parent[i] = node, node = parent, z *= 2;
+      switch (i) {
+        case 0: x1 = x0 + z, y1 = y0 + z; break;
+        case 1: x0 = x1 - z, y1 = y0 + z; break;
+        case 2: x1 = x0 + z, y0 = y1 - z; break;
+        case 3: x0 = x1 - z, y0 = y1 - z; break;
+      }
+    }
+
+    if (this._root && this._root.length) this._root = node;
+  }
+
+  this._x0 = x0;
+  this._y0 = y0;
+  this._x1 = x1;
+  this._y1 = y1;
+  return this;
+}
Index: node_modules/d3-quadtree/src/data.js
===================================================================
--- node_modules/d3-quadtree/src/data.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/data.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,7 @@
+export default function() {
+  var data = [];
+  this.visit(function(node) {
+    if (!node.length) do data.push(node.data); while (node = node.next)
+  });
+  return data;
+}
Index: node_modules/d3-quadtree/src/extent.js
===================================================================
--- node_modules/d3-quadtree/src/extent.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/extent.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,5 @@
+export default function(_) {
+  return arguments.length
+      ? this.cover(+_[0][0], +_[0][1]).cover(+_[1][0], +_[1][1])
+      : isNaN(this._x0) ? undefined : [[this._x0, this._y0], [this._x1, this._y1]];
+}
Index: node_modules/d3-quadtree/src/find.js
===================================================================
--- node_modules/d3-quadtree/src/find.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/find.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,70 @@
+import Quad from "./quad.js";
+
+export default function(x, y, radius) {
+  var data,
+      x0 = this._x0,
+      y0 = this._y0,
+      x1,
+      y1,
+      x2,
+      y2,
+      x3 = this._x1,
+      y3 = this._y1,
+      quads = [],
+      node = this._root,
+      q,
+      i;
+
+  if (node) quads.push(new Quad(node, x0, y0, x3, y3));
+  if (radius == null) radius = Infinity;
+  else {
+    x0 = x - radius, y0 = y - radius;
+    x3 = x + radius, y3 = y + radius;
+    radius *= radius;
+  }
+
+  while (q = quads.pop()) {
+
+    // Stop searching if this quadrant can’t contain a closer node.
+    if (!(node = q.node)
+        || (x1 = q.x0) > x3
+        || (y1 = q.y0) > y3
+        || (x2 = q.x1) < x0
+        || (y2 = q.y1) < y0) continue;
+
+    // Bisect the current quadrant.
+    if (node.length) {
+      var xm = (x1 + x2) / 2,
+          ym = (y1 + y2) / 2;
+
+      quads.push(
+        new Quad(node[3], xm, ym, x2, y2),
+        new Quad(node[2], x1, ym, xm, y2),
+        new Quad(node[1], xm, y1, x2, ym),
+        new Quad(node[0], x1, y1, xm, ym)
+      );
+
+      // Visit the closest quadrant first.
+      if (i = (y >= ym) << 1 | (x >= xm)) {
+        q = quads[quads.length - 1];
+        quads[quads.length - 1] = quads[quads.length - 1 - i];
+        quads[quads.length - 1 - i] = q;
+      }
+    }
+
+    // Visit this point. (Visiting coincident points isn’t necessary!)
+    else {
+      var dx = x - +this._x.call(null, node.data),
+          dy = y - +this._y.call(null, node.data),
+          d2 = dx * dx + dy * dy;
+      if (d2 < radius) {
+        var d = Math.sqrt(radius = d2);
+        x0 = x - d, y0 = y - d;
+        x3 = x + d, y3 = y + d;
+        data = node.data;
+      }
+    }
+  }
+
+  return data;
+}
Index: node_modules/d3-quadtree/src/index.js
===================================================================
--- node_modules/d3-quadtree/src/index.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/index.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,1 @@
+export {default as quadtree} from "./quadtree.js";
Index: node_modules/d3-quadtree/src/quad.js
===================================================================
--- node_modules/d3-quadtree/src/quad.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/quad.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,7 @@
+export default function(node, x0, y0, x1, y1) {
+  this.node = node;
+  this.x0 = x0;
+  this.y0 = y0;
+  this.x1 = x1;
+  this.y1 = y1;
+}
Index: node_modules/d3-quadtree/src/quadtree.js
===================================================================
--- node_modules/d3-quadtree/src/quadtree.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/quadtree.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,73 @@
+import tree_add, {addAll as tree_addAll} from "./add.js";
+import tree_cover from "./cover.js";
+import tree_data from "./data.js";
+import tree_extent from "./extent.js";
+import tree_find from "./find.js";
+import tree_remove, {removeAll as tree_removeAll} from "./remove.js";
+import tree_root from "./root.js";
+import tree_size from "./size.js";
+import tree_visit from "./visit.js";
+import tree_visitAfter from "./visitAfter.js";
+import tree_x, {defaultX} from "./x.js";
+import tree_y, {defaultY} from "./y.js";
+
+export default function quadtree(nodes, x, y) {
+  var tree = new Quadtree(x == null ? defaultX : x, y == null ? defaultY : y, NaN, NaN, NaN, NaN);
+  return nodes == null ? tree : tree.addAll(nodes);
+}
+
+function Quadtree(x, y, x0, y0, x1, y1) {
+  this._x = x;
+  this._y = y;
+  this._x0 = x0;
+  this._y0 = y0;
+  this._x1 = x1;
+  this._y1 = y1;
+  this._root = undefined;
+}
+
+function leaf_copy(leaf) {
+  var copy = {data: leaf.data}, next = copy;
+  while (leaf = leaf.next) next = next.next = {data: leaf.data};
+  return copy;
+}
+
+var treeProto = quadtree.prototype = Quadtree.prototype;
+
+treeProto.copy = function() {
+  var copy = new Quadtree(this._x, this._y, this._x0, this._y0, this._x1, this._y1),
+      node = this._root,
+      nodes,
+      child;
+
+  if (!node) return copy;
+
+  if (!node.length) return copy._root = leaf_copy(node), copy;
+
+  nodes = [{source: node, target: copy._root = new Array(4)}];
+  while (node = nodes.pop()) {
+    for (var i = 0; i < 4; ++i) {
+      if (child = node.source[i]) {
+        if (child.length) nodes.push({source: child, target: node.target[i] = new Array(4)});
+        else node.target[i] = leaf_copy(child);
+      }
+    }
+  }
+
+  return copy;
+};
+
+treeProto.add = tree_add;
+treeProto.addAll = tree_addAll;
+treeProto.cover = tree_cover;
+treeProto.data = tree_data;
+treeProto.extent = tree_extent;
+treeProto.find = tree_find;
+treeProto.remove = tree_remove;
+treeProto.removeAll = tree_removeAll;
+treeProto.root = tree_root;
+treeProto.size = tree_size;
+treeProto.visit = tree_visit;
+treeProto.visitAfter = tree_visitAfter;
+treeProto.x = tree_x;
+treeProto.y = tree_y;
Index: node_modules/d3-quadtree/src/remove.js
===================================================================
--- node_modules/d3-quadtree/src/remove.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/remove.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,62 @@
+export default function(d) {
+  if (isNaN(x = +this._x.call(null, d)) || isNaN(y = +this._y.call(null, d))) return this; // ignore invalid points
+
+  var parent,
+      node = this._root,
+      retainer,
+      previous,
+      next,
+      x0 = this._x0,
+      y0 = this._y0,
+      x1 = this._x1,
+      y1 = this._y1,
+      x,
+      y,
+      xm,
+      ym,
+      right,
+      bottom,
+      i,
+      j;
+
+  // If the tree is empty, initialize the root as a leaf.
+  if (!node) return this;
+
+  // Find the leaf node for the point.
+  // While descending, also retain the deepest parent with a non-removed sibling.
+  if (node.length) while (true) {
+    if (right = x >= (xm = (x0 + x1) / 2)) x0 = xm; else x1 = xm;
+    if (bottom = y >= (ym = (y0 + y1) / 2)) y0 = ym; else y1 = ym;
+    if (!(parent = node, node = node[i = bottom << 1 | right])) return this;
+    if (!node.length) break;
+    if (parent[(i + 1) & 3] || parent[(i + 2) & 3] || parent[(i + 3) & 3]) retainer = parent, j = i;
+  }
+
+  // Find the point to remove.
+  while (node.data !== d) if (!(previous = node, node = node.next)) return this;
+  if (next = node.next) delete node.next;
+
+  // If there are multiple coincident points, remove just the point.
+  if (previous) return (next ? previous.next = next : delete previous.next), this;
+
+  // If this is the root point, remove it.
+  if (!parent) return this._root = next, this;
+
+  // Remove this leaf.
+  next ? parent[i] = next : delete parent[i];
+
+  // If the parent now contains exactly one leaf, collapse superfluous parents.
+  if ((node = parent[0] || parent[1] || parent[2] || parent[3])
+      && node === (parent[3] || parent[2] || parent[1] || parent[0])
+      && !node.length) {
+    if (retainer) retainer[j] = node;
+    else this._root = node;
+  }
+
+  return this;
+}
+
+export function removeAll(data) {
+  for (var i = 0, n = data.length; i < n; ++i) this.remove(data[i]);
+  return this;
+}
Index: node_modules/d3-quadtree/src/root.js
===================================================================
--- node_modules/d3-quadtree/src/root.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/root.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,3 @@
+export default function() {
+  return this._root;
+}
Index: node_modules/d3-quadtree/src/size.js
===================================================================
--- node_modules/d3-quadtree/src/size.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/size.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,7 @@
+export default function() {
+  var size = 0;
+  this.visit(function(node) {
+    if (!node.length) do ++size; while (node = node.next)
+  });
+  return size;
+}
Index: node_modules/d3-quadtree/src/visit.js
===================================================================
--- node_modules/d3-quadtree/src/visit.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/visit.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,16 @@
+import Quad from "./quad.js";
+
+export default function(callback) {
+  var quads = [], q, node = this._root, child, x0, y0, x1, y1;
+  if (node) quads.push(new Quad(node, this._x0, this._y0, this._x1, this._y1));
+  while (q = quads.pop()) {
+    if (!callback(node = q.node, x0 = q.x0, y0 = q.y0, x1 = q.x1, y1 = q.y1) && node.length) {
+      var xm = (x0 + x1) / 2, ym = (y0 + y1) / 2;
+      if (child = node[3]) quads.push(new Quad(child, xm, ym, x1, y1));
+      if (child = node[2]) quads.push(new Quad(child, x0, ym, xm, y1));
+      if (child = node[1]) quads.push(new Quad(child, xm, y0, x1, ym));
+      if (child = node[0]) quads.push(new Quad(child, x0, y0, xm, ym));
+    }
+  }
+  return this;
+}
Index: node_modules/d3-quadtree/src/visitAfter.js
===================================================================
--- node_modules/d3-quadtree/src/visitAfter.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/visitAfter.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,21 @@
+import Quad from "./quad.js";
+
+export default function(callback) {
+  var quads = [], next = [], q;
+  if (this._root) quads.push(new Quad(this._root, this._x0, this._y0, this._x1, this._y1));
+  while (q = quads.pop()) {
+    var node = q.node;
+    if (node.length) {
+      var child, x0 = q.x0, y0 = q.y0, x1 = q.x1, y1 = q.y1, xm = (x0 + x1) / 2, ym = (y0 + y1) / 2;
+      if (child = node[0]) quads.push(new Quad(child, x0, y0, xm, ym));
+      if (child = node[1]) quads.push(new Quad(child, xm, y0, x1, ym));
+      if (child = node[2]) quads.push(new Quad(child, x0, ym, xm, y1));
+      if (child = node[3]) quads.push(new Quad(child, xm, ym, x1, y1));
+    }
+    next.push(q);
+  }
+  while (q = next.pop()) {
+    callback(q.node, q.x0, q.y0, q.x1, q.y1);
+  }
+  return this;
+}
Index: node_modules/d3-quadtree/src/x.js
===================================================================
--- node_modules/d3-quadtree/src/x.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/x.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,7 @@
+export function defaultX(d) {
+  return d[0];
+}
+
+export default function(_) {
+  return arguments.length ? (this._x = _, this) : this._x;
+}
Index: node_modules/d3-quadtree/src/y.js
===================================================================
--- node_modules/d3-quadtree/src/y.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-quadtree/src/y.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,7 @@
+export function defaultY(d) {
+  return d[1];
+}
+
+export default function(_) {
+  return arguments.length ? (this._y = _, this) : this._y;
+}