[#170] use `requestAnimationFrame` as default implementation for the game loop

* will fallback to `setTimeout` if not supported
* also uses `Date.now()` instead of `Date.getTime()`
Revert "Forgot this last one during final update !"

This reverts commit 530e9d9468a2c7711cd41cf2537263e23987d3c3.
[#170] fixed fallback to setTimeout/clearTimeout on browser version not implementing CaF
[#170] fixed an issue where the new game loop was potentially started before the previous one was stopped
[#170] added support for frame skipping when using RaF (through me.sys.fps)
[#170] cleaned-up examples and modified Changelog