Implement loop points within MIDI files

[nmlgc]

The game simply restarts a MIDI file from the beginning once it finished playing. That's also why the original MIDI files are rather large: They simply copy-pasted the loop section a couple of times to hide this nonexistent feature.

• Implement any or all of the common MIDI loop point conventions:
  • CC 2/4 (TH06-TH09)
  • CC 111 V=0/1 (RPG Maker)
  • CC 116/117 (XMI / EMIDI)
  • loopStart / loopEnd track markers (FF7 PC, HMI)
• Define loop points for the original MIDI files

[nmlgc]

I'll need to define correct loop points for the Sound Canvas VA recordings done in #9, so I might as well apply them to the MIDI backend while I'm at it.