added setRotation() to particle system

Here's a simple test using it: [code](https://dl.dropboxusercontent.com/u/32864004/dev/FPDemo/setRotationTest.zip) | [swf](https://dl.dropboxusercontent.com/u/32864004/dev/FPDemo/setRotationTest.swf)

Internal logic is separated, so if the user doesn't uses `setRotation()`, the matrix/draw step will be discarded and `copyPixels()` will be used instead.

Willingly this could be expanded to also include scaling.