Implement "VolumeValancer" mixer channels from the .ini file. Mixers are
now recursive, with the master and voice channels being parent nodes
(this seems to be hardcoded in system 4, or at least I haven't found
where the hierarchy is specified).
Also implement .wai file support (needed for mixer channel info on sound
files).
Replace SDL_mixer with an audio implementation using libsndfile,
sts_mixer (a single-file header library) and SDL's basic audio
interface.
This allows for much more flexibility in controlling audio playback.
Fading is now properly implemented, as well as various other functions
from the SACT2/KiwiSoundEngine interface.
sts_mixer can support recursive mixing, so it will be possible to
implement the "VolumeValancer" mixer channels specified in
System40.ini in the future (once I figure out how the mapping of audio
files to mixer channels is supposed to work).
Nunuhara Cabbage