[Feature Request]: Support XDG base directory specification #467

Feature Description

expose publish creates a new configuration file in ~/.expose/config.php.

This is another directory in my home dir, which gets pretty crowded.
On Linux the XDG Base Directory Specification solves this problem by providing standard directories - including ~/.config/ for configuration files.

It would be nice if expose would follow that specification and store its configuration in $XDG_CONFIG_HOME when this environment variable is set, and falls back to ~/.config/ if it is not set.
A fallback to ~/.expose for existing installations would be necessary as well.

Is this feature valuable for other users as well and why?

Making backups of one's configuration is easier because users only have to copy ~/.config.