Animation support

[mcvicar]

Not sure if it's worth having an animation module?

• Using CSS keyframes is reportedly faster than using straight JS, http://joehewitt.com/2011/10/05/fast-animation-with-ios-webkit - so it might require a fallback for iOS 4 to begin with.
• JavaScript-based animations should be limited to UI updates at ~17ms, which is equivalent to 60fps, which is the fastest most displays will refresh anyway. So we would neeed to keep track of the time since the last UI update and don’t do anything if 17ms haven’t passed.
• Perfomance issues with textures that are larger than 1024x1024 pixels
• Could use requestAnimationFrame instead of setTimeout / setInterval