Collisions updated:
- Mixed Collidable and Gravitatable on one component called Kineticable.
- Created a Circle module.
- Updated how SAT separates rectangles.
- SAT passes to Kineticable the side of where the collision is happening and can be obtained, for example:
	this.kineticable.isTouching(SAT.BOTTOM)
Fixed comments.
Merge pull request #125 from spilgames/#123-mix-collidable-and-gravitatable

Collisions updated: