web: Create man page with groff rather than man2html.

The man2html project is dead, as is the link on the osl web page. The
URL mentioned in the info of the man2html package for Ubuntu-14.04
still works but might not be the most up to date page on the planet
any more:

	http://users.actrix.gen.nz/michael/vhman2html.html

In any case, it's a funny read. Needless to say that the link to the
sunsite FTP server is also dead.

This commit makes osl independent of man2html, simply by running groff
-Thtml instead of man2html. This even simplifies the Makefile a bit.

The patch also removes the dead link on the osl main page. We don't
need a replacement reference to groff because groff should be installed
on all systems anyway.