Reduce dot-file clutter by using XDG base directories (~/.config/ etc.)

[deltab]

Please don't add more dot-files (~/.coconfig, ~/.co) to the user's home directory; there's probably already far too many already there.

Instead, consider using the XDG Base Directory specification, which provides a standardized way to collect the config, data, and cache files of many programs into just a handful of directories.

See https://rubyworks.github.io/xdg/ for more, including a gem.