Add Pico-8 support

[phillipprado]

Describe the solution you'd like: I think it would be really great to tout Pico-8 cart support directly in Lemuroid.

Describe alternatives you've considered: There is already an app that let's you play Pico-8 titles on Android called P8 Player, and you can even play most of them in the browser, but having the functionality in Lemuroid would mean that if I want local copies of my games I would need one less closed-source app on my devices to do so.

Additional context: Just to clarify, I'm not suggesting we add the whole Pico-8 app from Lexaloffle.com into Lemuroid, just something like the Fake-08 emulator. Also, since Pico-8 carts are just png files, you can just point to the file itself for boxart instead of pulling it in from the web.

[Montoya]

I would also like to see this! It’s one more core and like you said the thumbnails are built in to the ROMs.

[Ferk]

There's an existing libretro core that could be used for this: https://github.com/Jakz/retro8