(FACT-272) Format facter --help to work with ronn

This commit updates the output of facter --help to create markdown that
can be converted to a man page via ronn.
(FACT-272) Update manpage based on facter --help
Merge pull request #646 from adrienthebo/doc/facter-2/fact-272-update-manpage

Doc/facter 2/fact 272 update manpage