doc: replace pandoc-"Markdown" with real manpages

doc: replace pandoc-"Markdown" with real manpages

Trying to install pandoc on an x86-64 Debian stable system says:
> Need to get 15.2 MB of archives.
> After this operation, 117 MB of additional disk space will be used.

My laptop is on metered Internet, now, and low on disk space, so
installing pandoc is too expensive.

There's also dozens of incompatible Markdown flavors out there,
most of which don't really handle manpages.

Updating the website now requires olddoc 1.8.0 (which is much
smaller than pandoc), but I'm the only one with that burden.  On
the flipside more users can update and read the manpages locally
without extra software, since nearly every developer's *nix
system has man(1) command, unlike pandoc.