Combine SGML files into one.

This version is probably not a valid SGML file any more.  That's OK,
because now I'm going to start translating to org-mode.
Make copy of SGML version that will be edited into org-mode format
Preliminary translation to org-mode. Many bits of SGML markup remain.

I've dropped the Command Reference and Option Reference, since their content
would duplicate the official GnuPG documentatation.

I also removed the text of the GNU FDL 1.1; we can link to it or restore
the text later.
Convert more SGML markup to org-mode

org-mode offers fewer markup semantics than DocBook -- there's
no <application> or <prompt> in org-mode -- but I decided to just
grit my teeth and discard that information.  If we need it back, we'll
have to restore it from scratch using whatever features org-mode offers.
Convert embedded image and table to org-mode; fix two links
Fix an itemized list; tweak the image and table a bit