WAV Trigger performance improvements and update

Just posted v1.28 of the WAV Trigger firmware that dramatically improves the quality of the built-in track fades, and MIDI attack and release volume fades. Previously, volume was adjusted on a per audio buffer basis, resulting in small steps in volume that produced slight, but sometimes noticeable, distortion during fades. The new version now adjusts volume on a per sample basis, producing much smoother dynamic volume adjustments.

I also nailed a couple of subtle issues with interrupt priorities that caused random audio glitches when maxing out 14 voices repeatedly, such as rapidly playing lots of MIDI notes/chords with long release times.

Finally, this new version implements the MIDI Sustain Pedal controller, to make the WAV Trigger even more of a musical instrument.

As I mentioned previously, I'm currently working on support for seamless looping, eventually to include adjustable loop length and starting positions. Loops take more memory than voices, so adding loops will reduce the number of traditional voices. The first implementation will likely be a separate firmware release that supports say 4 independent loops and 8 traditional voices. Exact allocation TBD.