Narrowphase lookup table

Lookup collision resolution methods based on the shape type bits.
Cache the function, not the key
added property world.emitImpactEvent
Merge branch 'feature/narrowphase-lookups' of https://github.com/timrwood/p2.js into timrwood-feature/narrowphase-lookups
fixed .newShapeCollisionMask bug in Demo, thanks @timrwood for noticing it!
doc lockconstraint
using crossLength in FricitonEquation instead of ugly hack
updated readme
Updated PrismaticConstraint to new Equation formulation. Now it accepts optional arguments .localAnchorA/B and .localAxisA instead of the old ones
changed number of iterations in circles demo
changed default damping to 0.01 in Body
updated readme
added backwards compatibility functions .capsulePlane and .convexPlane to Narrowphase
updated readme
updated builds
docs
exposed .localAnchorA/B and .localAxisA in PrismaticConstraint
serializer bugfix for prismatic parameters
updated readme
changed default damping to 0.1