Trial -based docs organization

Attached is a proof-of-concept version of postgres.sgml, which shows how
the documentation could be organized by enclosing several <Book>s in a
<Set>. You can plug it in in place of the existing one and do make
postgres.html to see how it looks.

There's no rule to get an RTF version, so you have to use

jade -D ref -D ../graphics -d /where/ever/docbook/print/docbook.dsl \
  -t rtf postgres.sgml

by hand. (Well, you would have figured that out yourself.)

Let me know what you think.

--
Peter Eisentraut                  Sernanders väg 10:115
peter_e@gmx.net                   75262 Uppsala
http://yi.org/peter-e/            Sweden