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 nowadays and already low on
disk space, so installing pandoc is not realistic.  Maybe it
wasn't realistic to other hackers with limited resources in the
past.

There's also dozens of subtly incompatible Markdown flavors out
there, most of which can't really handle manpages.  Anyways,
roff isn't too bad and at least groff is well-documented.

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.