Four note harmonic structures

[OscarSouth]

The scope of the work and research underpinning it has been intentionally limited to three note (triadic) structures including fundamental tone. This scope could be logically expanded to three note structures OVER a fundamental tone (inside which, three note structures are a subset). This would present a great deal more interesting possibilities.

The existing codebase is partially written with this eventual expansion in mind, although how to implement the Machine Learning functionality effectively on on 7th chords will require some creative thought.

[OscarSouth]

All of the type instances for chords of any number of notes now exist -- I think it should be possible to extend the live generative parts out to use them.