Implement basic melody generation

[oubiwann]

Tasks, from page 82 of The Complete Musician, Fourth Edition:

• Start on one member of the tonic triad (e.g, 1, 3, or 5)
• End with the two-pitch pattern 2, 1 or 7, 1
• Limit the total tonal range of the melody (span of pitches) to the interval of a 10th
• Set most of the tonal activity in the range of a 6th
• Move primarily by one step
• Optionally, (less frequently) steps can be in thirds, fourths, or fifths
• When doing such disjunct steps, do more thirds than the others
• Limit larger jumps to be smaller than a perfect 5th
• Don't make dissonant leaps
• Don't leave tensions unresolved
• After leaps, consider using a change in direction to fill in the tonal jump (the larger the jump, the more important this is)
• Do not do multiple large jumps in a row
• After doing two small jumps in a row (i.e., two jumps by thirds), change direction.
• Avoid repeated notes and patterns
• Aim for smooth and continuous shapes (ascending / descending patterns)

Bugs in implementation:

• Length of melody is not always what is expected
• The final note is not always the tonic
• Notes are sometimes repeating, despite attempts to codify the prevention of this
• Every once in a while, the generated melody gets an index error (when trying to lists:nth)
• The initial scale length isn't getting extended to a 10th
• Need to implement proper melody inversion
• Need to end melody inversion on tonic