Support $XDG_CONFIG_HOME or System ENV paths

[bcomnes]

Home folder dot files are out of control. Would you be open to supporting alternate config locations?

There are two schools of thought on the matter:

• $XDG_CONFIG_HOME aka ~/.config https://github.com/sindresorhus/xdg-basedir
• Operating system recommended locations (linux$XDG_CONFIG_HOME, ~/Library for osx etc) https://github.com/sindresorhus/env-paths#pathsconfig