[Groff] left navigation within www.tmac

[Gaius Mulley]

Hi,

I've added three new macros to www.tmac which implement left hand side
navigation links for the text on the right hand side. Many thanks to
Keith and Tadziu for showing me how to overload SH, LP, NH
etc. Currently this mechanism only works with -ms and -mwww and -Thtml
but there is no reason why it couldn't be extended to other macro sets
and other devices. Anyhow an example of its usage is implemented in
doc/webpage.ms and the macros are documented in tmac/groff_www.man.

Here is the ChangeLog

        * doc/Makefile.in: separate rule for webpage.html so that
          extra command line options can be passed to grohtml.
        * doc/groff.css: changed all margins to 0%.
        * doc/webpage.ms: now uses new macros ALN, LNS and LNE
          so that left navigation is exploited. Also updated webpage
          to contain new sections on licences, mailing lists, cvs/ftp
          access, groff dependencies and bug reports.
        * tmac/groff_www.man: documented the new macros ALN, LNS and
          LNE.
        * tmac/www.tmac: implemented the new macros ALN, LNS and LNE.

Gaius