Rename a file or directory.
If either src_dir_fd or dst_dir_fd is not None, it should be a file
descriptor open to a directory, and the respective path string (src or
dst) should be relative; the path will then be relative to that
directory.
src_dir_fd and dst_dir_fd, may not be implemented on your platform.
If they are unavailable, using them will raise a NotImplementedError.