Returns the directory to use for program runtime data for the current user with a fallback for older OS:es.
See Source File
Boost Software License 1.0
Copyright (c) 2020, Joakim Brännström. All rights reserved.
Joakim Brännström (joakim.brannstrom@gmx.com)
This module contains functions to extract XDG variables to either what they are configured or the fallback according to the standard at [XDG Base Directory Specification](https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html).