Giant Quadtree is 2D collision Detection Without Boundaries

A quadtree is a data structure which segments 2D space to reduce the cost of collision detection.
Generally, a quadtree subdivides space as more elements occupy it. Giant Quadtree does this and adds a little twist:
it grows outwards whenever an element is added outside the current boundaries. This means collision detection
without boundaries.

An Example

In this example, we'll insert a box to the quadtree, and then check an area which the box overlaps for objects
to retrieve it again.

``javascript
var tree = Quadtree.create();
var myBox = { left: 0, top: 0, width: 100, height:100 };
tree.insert(myBox);
var objs = tree.get(0, 0, 10, 10);
console.log(objs[0] === myBox); // outputs true
`

Use

For plain JavaScript applications, use the dist/quadtree.js, which will inject the Quadtree object to the global
scope. If you're using NodeJS (or any system that uses the export/require pattern), use dist/quadtree-module.js,
as it exports the Quadtree object.

API

In the API Quadtree (capitalized) refers to the module object and quadtree (lowercase) refers to a
Quadtree instance which is created via Quadtree.create.

$3

Constructor function which returns a new Quadtree instance. By default, the starting height and width are
10,000 pixels.

`javascript
var myTree = Quadtree.create();
// 1. add a bunch of rectangles using myTree.insert
// 2. find a bunch of collisions using myTree.get
// 3. clear the tree for the next step using myTree.clear
// repeat steps 1 to 3
`

$3

Inserts a rectangle to the quadtree. A rectange is any object which has a width, height, left, and top
property. This object may have any other properties (none of them will be modified by the Quadtree).

`javascript
var myTree = Quadtree.create();
// Add a 100x100 box with the top left corner at 0,0
myTree.insert({left: 0, top: 0, width: 100, height: 100});
// Add a 100x100 box overlapping the previous with the top left corner at 50,50
myTree.insert({left: 50, top: 50, width: 100, height: 100});
`

$3

Returns all rectangles which intersect the given dimensions. This method useful for finding collisions.

`javascript
var myTree = Quadtree.create();
myTree.insert({left: 0, top: 0, width: 100, height: 100});
myTree.insert({left: 50, top: 50, width: 100, height: 100});
var boxes = myTree.get(60, 60, 100, 100);
// boxes will contain both of the inserted boxes since they intersect the boundaries of the get query
`

$3

Clears the quadtree of all objects.

`javascript
var myTree = Quadtree.create();
myTree.insert({left: 0, top: 0, width: 100, height: 100});
myTree.insert({left: 50, top: 50, width: 100, height: 100});
var boxes = myTree.get(60, 60, 100, 100);
console.log(boxes.length); // 2
myTree.reset();
var boxes = myTree.get(60, 60, 100, 100);
console.log(boxes.length); // 0
`

$3

Clears the quadtree, but retains any elements that fall within the given dimensions.

`javascript
var myTree = Quadtree.create();
myTree.insert({left: 0, top: 0, width: 100, height: 100});
myTree.insert({left: 50, top: 50, width: 100, height: 100});
var boxes = myTree.get(60, 60, 100, 100);
console.log(boxes.length); // 2
myTree.prune(-10, -10, 120, 120); // keep everything that's contained in these boundaries
var boxes = myTree.get(60, 60, 100, 100);
console.log(boxes.length); // 1 (the first box that was inserted)
``