Support for XDG base directory specification

[siimhs]

Would it be possible to support XDG base directory specification?

If you are not familiar with XDG then there is a nice blog that explains benefits of it.

Currently .digidocpp folder is cluttering a bit my $HOME.

Found a place in source where that is set. I don't fully understand the purpose of that folder, but I sense that it is either a cache or application data.