add game-music-emu Formula.

Game_Music_Emu is a collection of video game music file emulators that support
the following formats and systems:
 AY         ZX Spectrum/Amstrad CPC
 GBS        Nintendo Game Boy
 GYM        Sega Genesis/Mega Drive
 HES        NEC TurboGrafx-16/PC Engine
 KSS        MSX Home Computer/other Z80 systems (doesn't support FM sound)
 NSF/NSFE   Nintendo NES/Famicom (with VRC 6, Namco 106, and FME-7 sound)
 SAP        Atari systems using POKEY sound chip
 SPC        Super Nintendo/Super Famicom
 VGM/VGZ    Sega Master System/Mark III, Sega Genesis/Mega Drive,BBC Micro