refactored verletIntegration to integrate shapes, removed entities position and oldPosition
added tests and fixed bugs of getDisplacement
added tests for overlaps
I started writing collision processing, and tested satisfyLineConstraint
eliminated the sqrt in satisfyLineConstraints when no change is needed
fleshed out the rest of detailedCollision and everything should expect a float or double now
added a moveShape method
Implemented very basic collision response. The physics engine is now fully implemented.