Update README.md
mechanism for reusing damping coefficients, will remove some garbage collection load
changed stiffness param in concave demo
changed restitution demo to restitution=1.0
world doc
turning off body damping in asteroids demo
removed unused code from car demo
Added property .fixedRotation to Body and implemented support in World. Fixes #37. Ping @photonstorm
added preliminary AABB class
added premliminary method .computeAABB to Shape
fix: undefined check had incorrect return value
Merge pull request #42 from wellcaffeinated/patch-1

fix: undefined check had incorrect return value
Added JSONFileFormat class and updated serializer
consistency check when adding a Body to, or removing a Body from World
Equation optimization
optimized narrowphase
using array of object keys in Narrowphase.collidingBodiesLastStep. This enables optimization in V8
using garbage free Array.splice
no need to compute gravity vector length in World.step any more
added property .applyGravity to World