Tue May 30 21:33:45 CEST 2017

midi voice control

Voice update functions should be executed on each midi event:
- note on
- note off
- cc

Also, a 200kHz modulation tick might be good.

The easiest way to implement is to cache the state in global
variables, such that update functions for each voice can just use
what's needed.

First: program control.  This is standard midi.