Move config file according to XDG specification

[diimpp]

$XDG_CONFIG_HOME defines the base directory relative to which user specific configuration files should be stored. If $XDG_CONFIG_HOME is either not set or empty, a default equal to $HOME/.config should be used.
http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html

And it has .go extension when it's json.

[kytrinyx]

Thank you -- I was unaware of the specification about $XDG_CONFIG_HOME.

[kytrinyx]

freedesktop.org is open source / open discussion software projects working on interoperability and shared technology for X Window System desktops.

The exercism command line client is a command-line application and has nothing to do with desktop software or X Window System desktops. I've concluded that as such the $XDG_CONFIG_HOME environment variable does not apply.

I've opened a new issue for the extension issue.

Thanks for bringing these issues up.