XDG compliance

[Conaclos]

Hi :)

XDG base dirs

It could be nice to fit the XDG basedir specification.

• If .moc and .moc/config don't exist then the configuration is ${XDG_CONFIG_HOME:-$HOME/.config}/moc/config
• Runtime files (pid, socket, ...) can be placed at $XDG_RUNTIME_DIR
• Files such as equalizer, softmixer, last_directory, and playlist.m3u can be placed at ${XDG_CACHE_HOME:-$HOME/.cache}/moc

XDG user dirs

• Default value of MusicDir can be ${XDG_MUSIC_DIR:-~/Music}