The purpose of this package is to provide platform-specific paths for reading
and writing configuration, cache, and other data.

On Linux (`gnu/linux'), the directory paths conform to the XDG base directory
and XDG user directory specifications as published by the freedesktop.org
project.

On macOS (`darwin'), the directory paths conform to Apple's documentation at
https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPFileSystem/Articles/WhereToPutFiles.html.