MIDI note parameter support

[benjaminfox]

For #128, I'd like to extend this dataset to document MIDI note behaviour, which is especially helpful with drum machines.

I propose doing this by accepting device.triggers.csv files that use a different format than the existing dataset's device.csv files. I think this serves people who only want to read one kind of file, and people who want simple access to both kinds of files, equally well.

Here are some samples:

• A template, using a fictional drum machine
• Vermona's DRM1 MKIV, which otherwise has no documented MIDI CC behaviour
• Roland's TR-1000
• Elektron's Analog Rytm MKII
• Novation's DrumStation

These are the proposed columns:

Column	Required	Comment
manufacturer	✅	Must match containing directory
device	✅	Must match filename + .triggers.csv
section
sound_name	✅	Something like 'Bass drum', 'BD', etc.
sound_description		Use when sound_name is not self-explanatory. Caveats and warnings belong in the comments column.
midi_channel	✅	Must be either a valid MIDI channel number (1 through 16 inclusive), or one of: basic, omni, active.
note_number_min_value	✅	For sounds that are triggered only by a single note number, use that single note number. For sounds that are triggered by a continuous range of note numbers, use that range's lowest note number.
note_number_max_value	✅	For sounds that are triggered only by a single note number, use that single note number. For sounds that are triggered by a continuous range of note numbers, use that range's highest note number.
note_number_default_value		For sounds that are triggered only by a single note number, use that single note number. For sounds that are triggered by a continuous range of note numbers, where a default or preferred note number is specified, use that default or preferred note number.
comments		Caveats and warnings that don't fit in sound_description.
velocity_usage		The sound's variance with velocity (from 1 to 127 inclusive), documented using the MIDI Guide usage grammar (e.g. 1~127: Volume)

The valid special values in the midi_channel column mean:

• basic: The device's MIDI channel, when it only has an undocumented and single (either configurable or factory-set) channel.
• omni: The device receives on all MIDI channels, and doesn't distinguish between them.
• auto: Some multi-track/multi-instrument devices have a MIDI channel that routes to the currently-active track/instrument (Elektron, etc.); this value indicates the active routing channel should be used.

Some columns I didn't include:

• Anything about one-shot/gate behaviour: doesn't ride along with the MIDI note, and is entirely defined on the synth itself
• The note name (C#2, etc): I considered having two columns for this information (for the corresponding Yamaha and Roland pitch), but I feel that this places a burden on the documenter that's disproportionate to the value of recording this easily-computable information. The project website might compute and display this information for the convenience of visitors.

I'd be happy to hear any feedback on this approach.

[benjaminfox]

I'm moving ahead with this. Steps before merge:

• Add device.triggers.csv documentation to README.md
• Add device.triggers.csv documentation to CONTRIBUTING.md
• Change the tests to accept valid device.triggers.csv