Change man page src format from yodl to markdown.

Change man page src format from yodl to markdown.

This removes the yodl dependency, which is sometimes hard to track down.
Instead, this uses a python3 script that leverages the cmarkgfm library
to turn the source file into html.  Then, the script parses the html in
order to turn the tag stream into a nroff stream using a simple state
machine. While it's doing that it also implements one added format rule
that turns an ordinal list that starts at 0 into a description list
(since markdown doesn't have an easy description list idiom).