[Request] Add support for .m3u

[RiskyJumps]

For RetroArch to be able to swap discs on multi-disc games, an index file (.m3u) is required. The file is just a simple text file that lists all the .cue (for .bin/.cue) or .chd files (separated by newline characters).

For more info, please look at: multiple-disk-games

[tony971]

#362 (comment)

#17 (comment)

[stenzek]

Implemented in f3df4f9

Needs a core file update to signal that DuckStation can accept m3u files now - you can edit it yourself in the meantime.