Add lots of DSC comments, and change the DSC version to 3.0, which has been

Add lots of DSC comments, and change the DSC version to 3.0, which has been
current since 1990.  The only obvious change from this is that gv now displays
the document title.

There's a slight bug here at the moment in that the backend emits
%%DocumentNeededResource and %%IncludeResource for each subfont of a
PostScript font, even if that PostScript font has been requested already.
This is wasteful but, as far as I can see, not actually disallowed, and
is easier than de-duping the font list.

git-svn-id: svn://svn.tartarus.org/sgt/halibut@4551 cda61777-01e9-0310-a592-d414129be87e