libpq/libpq++ result function reorganization

I have applied the following patch to the docs. Previously, all the
PQexec() result functions where listed in one long list which I found
hard to understand.

I created subsections, <sect2>, for main routines, SELECT information
routines, SELECT value routines, and non-SELECT routines.

I did this for libpq and libpq++. The other interfaces didn't have this
problem.

Tweeking welcomed. I tested the HTML output here with my old sgmltools
install and it looked OK.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
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