Add an extension to support MSADPCM buffer formats
Expand the sign bit on the initial MSADPCM delta value
Use maxi to clamp an int to a lower-bound
Use specialized methods for converting IMA4 and MSADPCM to ALshort

Since the decoder methods already convert to ALshort, there's no need to use a
temp buffer that's just going to copy directly to the destination.
Use specialized methods for converting ALshort to IMA4 and MSADPCM

As before, to avoid unnecessary direct copies
Allocate enough temp space for the ADPCM decoders and encoders