RFP: python3 packages cmarkgfm and commonmark

[Jari Aalto]

I wa checking the latest rsync and in order to build it, would someone
package these for cygwin:

    Configure found the following issues:

    - You need python3 and either the cmarkgfm OR commonmark python3 lib in order
      to build man pages based on the git source (man pages are included in the
	official release tar files).

Thanks,
Jari