Bugfix: lower-accuracy norms cause bypass flickering in
deferredFragShader.glsl.
Initial creation of SoundEvent.
Initial creation of AbstractSoundEvent.
Initial creation of SamplePlaybackEvent.
Initial creation of GPUResidentMOD.
Initial creation of MusicPlaybackEvent.
Added finalize() implementation of GLTexture.
Optimized and partially redesigned SoundSystem.
Updated Mission for partial BG music support (no bosses).
Cleanup.