Add quantizer generator support

[oubiwann]

This will allow users to emulate this type of modular synth hardware:

• https://www.youtube.com/watch?v=xnUFtQC0nks
• https://ornament-and-cri.me/

(thanks to @brianstarke for the links!)

Depends on:

• 114

• 110

• https://github.com/lfex/loise/issues/53
• https://github.com/lfex/loise/issues/54
• https://github.com/lfex/loise/issues/60
• https://github.com/lfex/loise/issues/65

Tasks:

• [ ] Add rand-note function
  • [ ] gets next random number from stateful random generator (see #114)
  • [ ] with appropriate max value (e.g., 127)
  • [ ] optionally filter it
• [ ] Add filters supporting
  • [ ] musical key
  • [ ] musical key and scale
  • [ ] upper and lower bounds
  • [ ] an explicit set of notes
• [x] Implement core concepts in undertone (borrowing implementation ideas from Extempore)
  • [x] #116
  • [x] #117
  • [x] #118
  • [x] notes