Fix build break introduced by git cherry-pick
Add BitDepth enum, setting to AudioSettings class

Unit tests added as well.
Add PcmSampleBuffer class
Option for bit-depth (for raw PCM files)
Audiofile SampleSource uses PcmSampleBuffer
PCM SampleSource uses PcmSampleBuffer
WAVE SampleSource supports multiple bitrates (experimental)
Add --endian option for raw PCM data
Remove code for PCM sample conversion from SampleBuffer

No longer necessary now that we have PcmSampleBuffer class.