Animation fixes

• Fixed #12 which was an issue around the stopAngle when the pointerAngle was not the default and the wheel stopping at unexpected places.
• Fixed #8 which was an JS error if stopAnimation was called before the animation had run for the first time
• Discovered an issue with using the Greensock tick event for the animation loop where at times it did not appear to render the last frame (so final state of the wheel). Changed to use onUpdate() callback instead.