Implemented the core functionality for the Box2D physics system
Initial box2d commit
commit box2d
Box2D core implementation

This is the initial commit for the box2d core functionality. There is
still some work that needs to be done with physics contact listeners,
but for now the physics system is working as intended.

NOTE: The previous physics system is still lingering in the code, and
must be removed at a later time.
Box2d core implementation

Core box2d implementation is now in the game!
box 2d implementation