port music features from metroidvania project and merge FM synth into mainline

[clydeshaffer]

This PR upgrades the music system of the SDK to use the new FM synthesis firmware which provides 4 FM synth channels with 4 operators each.

Other new music features include:

• optionally include note velocities in midi conversion
• each operator in each channel has its own configurable decay and sustain parameters to allow different "instruments"
• asset.cfg files allows for setting overrides on conversion options per file
• specify instrument selections for channels in asset.cfg
• sound effects that take over a channel and then give it back to the music
• song stack to allow incidental music to play and then return to the previous song