Changes to MIDIIntermediateRepresentations need to be restructured and clarified

[codaich]

• Documentation of many of the changes is often sparse and unclear, and is sometimes seemingly incorrect.
• Some of the new fields are deceptively named.
• Some of the changes cause data to be treated in a very dangerous and sloppy way.
  • The standard prior to the changes was that each public field was calculated by a clearly marked private method that uniquely set it, and no (non-static) other method should alter its values; this standard should be maintained.
  • In a complex class like this, data and processing need to be very, very well documented and treated in a very, very safe and clear way.

[codaich]

• To give one example, the way the (before I fixed them in Commit 1fa0a08) vertical_interval_chart, unison, total_unison_velocity and channel_track fields were used was quite confusing and potentially dangerous.
• I've now clarified (and fixed a minor bug in) these fields and the mehtods relating to them, so they no longer need to be addressed in particular, but all other new content in this class still needs to be similarly improved.

[codaich]

all_note_info and its calculation in particular needs to be better documented.

[codaich]

Should also validate, clean up and document other related classes in jsymbolic2.featureutils (and other packages too, perhaps).

[codaich]

Issue fixed in commit [b3fefc4]. Issue closed.