Add missing const's.
voice_removal: Tabs to spaces.
crossfade: Use Index<float> for buffers.
echo: Use Index<float>.  Cleanups.
ladspa, mixer: Use Index<float>.
speed-pitch: Revise some messy logic.  Use Index<float>.
bs2b, crystalizer, stereo, voice removal: Update for effect API changes.
compressor: Use Index<float>.
resample, sox-resampler: Use Index<float>.
sdlout: Use RingBuf.