BUGFIX: Corrected PingPong animation timing being incorrect on the 1st and last frames

After the first animation cycle through the frames when ping ping is
activated, the 1st and last frames were both being displayed 2x longer
than they should be.
Added some methods for setting color tint, rotating the z axis of the sprite, etc

Added the following methods:

setColor() - Sets the color tint of the sharedMesh quad at runtime

rotate() - Rotates the sprite about the z-axis

playAnimation() - Starts an animation only if one is not currently
playing, or the one requested is not the one currently playing.
Merge pull request #4 from bncastle/master

BugFix for PingPong animation and added additional methods to SKSprite