Add XDG Support

[wtetzner]

Add support for reading/writing data, config files, etc. using the XDG spec: https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html

https://stackoverflow.com/questions/43853548/xdg-basedir-directories-for-windows/49783629#49783629

[gyrovorbis]

A fair reaquest. lol.