Add support for display of a specific frame
Add cancelAnimationFrame method, address bugs related to stopping the animation

Prevent multiple calls to play creating more than one executing loop,
and resolved issue that FPS was not applied immediately; both as the
timer object was never set.
Make animations stop immediately rather on next frame iteration -
resolves issue with needing to call play twice twice after calling
'stop' twice.
Update README.md
Merge pull request #5 from NeilCross/master

Added support for programmatically skipping to a specific frame.  Fixed issue with reversing playback.