Parse Gecko Code contents

[NickCondron]

Looks like slippi-js is implementing this feature (https://github.com/project-slippi/slippi-js/compare/feature/gecko-list), so we probably should too. Documentation on gecko codes is oddly hard to find, but I found this:

https://gamehacking.org/faqs/wiicodetypes.html

https://web.archive.org/web/20191211012905/http://geckocodes.org/index.php?arsenal=1

https://github.com/FIX94/Nintendont/blob/master/codehandler/codehandleronly.s

https://github.com/dolphin-emu/dolphin/blob/master/Source/Core/Core/GeckoCode.h

Or we can just copy what fizzi did

[hohav]

I have no objection to doing this, but probably won't work on it myself. If someone else wants to, let's discuss design before you get too deep in the implementation.