Add support for DiamondWare DWM

[Sembiance]

As far as I can tell, the DiamondWare DWM format that is very close to MIDI.

Sample files here: https://sembiance.com/fileFormatSamples/music/diamondWareDigitizedMusic/

This project talks a bit about the DWM files and how it relates to MIDI: https://github.com/Moufinure/quiver_ripper This DOS software can convert MIDI to DWM: https://archive.org/details/DiamondWaresSoundToolKit_1020

Not sure how hard it would be to convert back to MIDI, but it would be awesome if such a converter were to exist.