MIDI processing toolchain based around envelopes and controllers.
- Cantina common (submodule)
- Change handling of ADSR State velocity from Physics (too unstable) to a simple slider. (obvious in retrospect, but hey I got to learn some stuff before it turned into a nightmare.)
- Move ownership of MIDI controllers to the envelopes, make a controller manager to dispatch input commands.
- Change Note and Control handling to Command pattern.