[Feature] Testing and ideas for the new `export-roms` subcommand

[alucryd]

Hi guys, just merged my initial work on the export-roms subcommand. Right now it supports all the formats convert-roms does, as well as an additional special case for PS2 and OPL, that will convert the PS2 CUE/BIN CD games to ISO as OPL only supports ISOs. I also added a -g flag to only export 1G1R games.

I'm open to ideas as far as formats and filters go, formats can be lossy here so the sky is the limit as long as there's an open-source tool for it, preferably cross-platform.

And as usual, testing is greatly appreciated!