custom shape enhancement

This is a follow-up task of OFFICE-1867:

> Copied from office-comment list

> Original author: Chris Nokleberg
> Original date: 21 Jan 2006
> Original URL (for information only - broken link): http://lists.oasis-open.org/archives/opendocument-users/200601/msg00014.html

It covers this suggestion from the comment:

> I would suggest amending the enhanced-path specification to allow for
> additional commands which would indicate that a particular subpath
> should be lighter or darker by a certain amount.