change constructors of constraints, contactmaterial. Added RigidVehicle + demo
minor docs fix
added initial AABB class, tests, and stub for Broadphase.prototype.aabbQuery
work on aabbQuery in NaiveBroadphase and stuff
flatten shape hierarchy
contact fixes
minor rigidvehicle update
initial work on Heightfield.prototype.getHeightAt
made tests work
minor heightfield test update