man: new man pages generated from gh-pages/man via pandoc

These man pages are generated from the Markdown man pages on the
gh-branch, in the `man` directory.  Pandoc is used to generate these
pages from the Markdown pages.

I'm not entirely pleased with how Pandoc is indenting the code
Synopsis section at the top, but I'm not quite sure how to fix that.

Accepting this commit means that we will change the workflow for
libfabric man pages:

1. The Markdown man pages in the `gh-pages` branch is the One
   Canonical Source of Truth.  I.e., all changes to man pages will be
   made in the Markdown pages on `gh-pages` (note: you can still do
   pull requests on the `gh-pages` branch).
1. A cron job will run (at Cisco for now, but it can run anywhere)
   that periodically examines the `gh-pages` branch for changes to the
   Markdown pages.  It generates a new nroff man page for any Markdown
   man page that was changed, and commits that new nroff man page into
   the libfabric `master` branch.

Hence, all the nroff pages in `master` will always be generated, and
will always be within N hours of being in sync with the Markdown pages
on the `gh-pages` branch.

Sidenote: N should be, at most 24, IMHO.  But it can be more frequent
than that.