issue2550966: fix suboptimal links in docs. I think I got the majority of them. Some links still don't resolve because they are gone and there is no replacement afaict. Also the check is picking up example links like: https://.../rest and http://localhost:8017/... which should not be checked but are.

This directory contains alternate front-ends for Roundup.

roundup.cgi
   This is a cgi-bin script.

ZRoundup
   This is a simple Zope frontend that installs as a regular Zope product.

See Roundup's doc/installation.txt for more info on installing these
frontends.