I had to redo how input is done entirely, so more than one source of input can be used for game inputs.
I added new inputs, menu_decide and menu_back. Return and escape still have their reserved status, sending menu_decide and menu_back, respectively. Other keys are reserved too, like arrows, to ensure users can always reconfigure input.
- Loading Discord RPC is now handled by `load/rpc.lua`
- Removed `presence` global, call `DiscordRPC:update()` directly with what needs updating
- Game doesn't crash anymore if the Discord RPC fails to load
- Added RPC variables in the gamemode superclass to let each gamemode handle its special case
- Implemented retry button*
- Escape on mode select sends you to title screen
- Escape on title screen closes the game
- Added "Exit Game" entry on title screen, closes the game when selected
*Pardon my angry comment in `scene/game.lua`.
* Added Ligne C89, now known as Marathon C89.
* Refactored all the Ligne modes to no longer use the "Ligne" name.
Ligne -> Race 40
Ligne A1 -> Marathon AX4
Ligne C89 -> Marathon C89
