BoundNodes do not use width and height for retrieve() calls

[Qqwy]

I am trying to use this QuadTree implementation as a collision detection algorithm with lots of tiles.

however, it seems that there is no special _findIndex() method in the BoundNode class. This means that no matter the size of the colliding object, only the top left corner will be used to determine what objects to retrieve.

This is easily fixable by adding an extra check in the retrieve() function as well as an extra function that simply returns all the contents of a certain node. I'll upload my own fix shortly.

[Qqwy]

I've created a pull request here: #7