xdg-cache-home

Path representing the base directory relative to which user-specific non-essential data files should be stored as described in the [XDG Base Directory Specification](https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html). Returns path based on the value of env-var `XDG_CACHE_HOME` (if set and representing an absolute path), else `(fs/path (fs/home) ".cache")`. When provided, appends `app` to the path.