MSVC fixes

Fixed compiler error in MSVC dealing with lambda return types (I guess
it can't deduce them?) and also signed/unsigned mismatches.
Audio mixing improvement
Adding in track count
Audio mixing
Added enemy blink when damaged
Added blinking to Enemy when damaged
Added Particle implementation
Iterating on Particle
Adding in Particle infrastructure to GameWorld
Added "action spot" to Entity

This allows an offset to be used when firing a weapon. In this case its
important for Mega Man to shoot bullets from his arm cannon instead of
the middle of his body. His body is ready.
More infrastructure for Particle support
Added position to particle as well as cloning
Implemented addition processing for particles
TEMPORARY: prototype particle in GamePlayState
Merge pull request #98 from zackthehuman/master

Particle infrastructure work