See mostly the git repository.

 * 1.21 - change shift to (...) = @_ form. update docs to better show
   how to use the interface.

 * 1.20 - BSD license, don't support Haiku OS (no link()), more web
   pages on how various filesystems make rename() problematic.

 * 1.18 - Changes from stdweird: octal mode support, :group support for
   _set_ownership, backup suffix, mtime modifiction.
