Adding an example for pixi renderer
Including pixi renderer in src
Fixing tabs and removing setInterval for updates in ticker
Updating comments at top of example
Throw error if pixi isn't defined
Updating art for example
Adding the option to pass a container to renderer when creating sprites
Removing require
Increasing viewport, removing body collisions
Adding documentation for the pixi renderer
Fixing JSHint errors
Updating grunt generated files
Removing duplicate physics source in example
Merge branch 'pr/71' into 1.0.0-rc1

Conflicts:
	src/behaviors/body-collision-detection.js
	src/behaviors/body-impulse-response.js
	src/behaviors/edge-collision-detection.js
	src/behaviors/sweep-prune.js
	src/core/behavior.js
	src/core/world.js
	src/util/pubsub.js