Engine:
+ Split PlaySound into PlaySound and LoopSound
+ Added overloaded versions of PlaySound/LoopSound that won't require voicepack parameter
+ LoopSound now allows multiple copies of the same sound to play looped and returns the channel used for playback (to stop them later)
+ StopSound now allows either a specific sound (single playback) or channel (single playback as well as looped playback) to be stopped
+ SoundChannel attribute for Gears to be used when looping sounds
