Add MSX support

[JZimz]

Support for MSX ROMs. RetroAchievements treats MSX1 and MSX2 as a single system, so we can probably do the same.

Extensions: .dsk, .mx1, .mx2, .rom, .cas, .m3u

Note: .rom is also used by Atari 5200 and Jaguar, but those aren't supported yet so no collision for now.

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