Function path_clean::clean

pub fn clean<P>(path: P) -> PathBufwhere
    P: AsRef<Path>,

The core implementation. It performs the following, lexically:

1. Reduce multiple slashes to a single slash.
2. Eliminate . path name elements (the current directory).
3. Eliminate .. path name elements (the parent directory) and the non-. non-.., element that precedes them.
4. Eliminate .. elements that begin a rooted path, that is, replace /.. by / at the beginning of a path.
5. Leave intact .. elements that begin a non-rooted path.

If the result of this process is an empty string, return the string ".", representing the current directory.