Support XDG_CONFIG_HOME directory layout on Linux

[sethwoodworth]

In linux, applications should follow the freedesktop standard, install user applications in XDG_DATA_HOME ~/.local/share/ and config files where specified by the XDG_CONFIG_HOME variable, usually defaulting to ~/.config/.

I installed scm_breeze and had to modify only three files to use XDG_DATA_HOME/XDG_CONFIG_HOME directories.

Standard

If I were to offer a PR supporting the basedir spec on linux platforms, would you consider it?

[ghthor]

Yeah, let's see it!