Improve COllision docs

Adds practical examples to the collision features introduced in #699 .
Move color and tint into new file
Refactor Color and remove Tint

This patch
- eliminates Tint and adds its capabilities to Color.  (Works with DOM now, since we don't need to worry about IE8 etc.)
- adds a new method (Crafty.assignColor) for converting any string representation of a color into rgb(a) components
- removes `Crafty.toRGB` in favor of this new method.
Merge pull request #770 from starwed/color-tint-refactor

Color, Tint refactoring
Fix for propogating 90deg rotations to child entities
Merge pull request #774 from FallSe7en/develop

Fix for propogating 90deg rotations to child entities
Merge pull request #768 from mucaho/collision_docs

Improve Collision docs