Support XDG Base Directory Specification

[jasonlyle88]

It would be nice if you would support the XDG base directory specification: https://specifications.freedesktop.org/basedir/latest/

For *nix based OSes, rather than automatically storing everything in ~/.inshellisense, following the XDG base directory specification, you would store your configurations in ${XDG_CONFIG_HOME:-$HOME}. Many projects choose to store in .inshellisense if XDG_CONFIG_HOME is not set, but inshellisense if XDG_CONFIG_HOME is configured.

Thanks for your consideration!