Configure command-line parameters for user-level control.

[blinks]

Default parameters should probably choose randomly. This would ideally get rid of a bunch of magic numbers, though.

Possible arguments:

• Time (4/4, 3/4, 6/8, etc.)
• Key (root and mode)
• Melodic motif (in Parsons code?)
• Parts (two bass parts? perhaps this could include the MIDI channel.)