Update to BBS documentation

[Truthkey]

Hello, everyone.

In this pull request I include tons of documentation on Birth by Sleep that I gathered while making the Ultimate Mix mod. This includes:

• Executable-only data structures.
• Memory-only data structures (might help people who mod with LUA).
• Updates on already documented formats.
• Some new file formats like config files for the ice cream minigame, the EXP 0 ability or Mirage Arena Bonuses.

Hopefully, it can be merged without issues.