VGM: Dual-chips support

[Wohlstand]

Looking the VGM specification: https://vgmrips.net/wiki/VGM_Specification we can see that here is a dual-chip support that allows to run two parallel chips for certain purposes.

Here I made the working of YM2612 (without this change, in current version you’ll hear high-frequency garbage rather proper song):
https://bitbucket.org/Wohlstand/game-music-emu/commits/493fbf77c1d534f2d901d575ad6dca76138c99c4

I going make this more clear and support dual-chip for other chips too include PSG. After works, I’ll post a pull-request.

Attachment - an example VGM file with dual YM2612 usage.

In parallel I working on MIDI2VGM utility with using of OPNMIDI’s backend and the attached song is the result of this tool. The file plays correctly on ZXTune player.

// Please assign me.

[Wohlstand]

Another sample dual-YM2612 VGM file

[Wohlstand]

Just now I have sent a pull-request: https://bitbucket.org/mpyne/game-music-emu/pull-requests/14/vgm-implement-dual-ym2612-support

[Michael Pyne]

I’ve sent you an invite to contribute to the repository as Bitbucket doesn’t allow me to assign you issues otherwise (and obviously, I’m comfortable with your being able to contribute and land patches on your own once reviewed).

[Michael Pyne]

Fixed via pull request 14