Feature: per-game wine prefix

[sparr]

With wine installed, the Linux itch client can install and run Windows games. I believe this is done by butler providing a Host that wraps the game binary in calling the wine binary. Doing just this results in every game sharing the default ~/.wine WINEPREFIX. I am proposing an option that will cause each game to get its own wine prefix.

This would probably need to be implemented in this repo to provide the option to users and pass it to butler, and in butler to handle that option and produce an appropriate Host.Wrapper.Env. I'm not sure if any changes to butlerd would be required.

I have some ideas for where the prefixes could go:

• ~/.wine/$GAMENAME
• $LIBRARYDIR/$GAMENAME/.wine
• $LIBRARYDIR/WINEPREFIXES/$GAMENAME

I'm up for implementing this if it would get merged and with a little guidance.