v3 of sphinx docs

[David Bremner]

This version includes a complete conversion of the existing manpages.
The conversion uses doclifter + custom python code + pandoc. It is
pretty much fully automated, so I can rebase against changes to the
nroff source if needed.  

On the other hand, it is fully automated, so there are bound to be a
few rough spots. If there are systematic things, I can fix the
conversion scripts; one offs can just be added to the series.

It does do a much better job of option indentation than the previous
version.

I think this is reaching the point where if anybody has any strong
objections to sphinx (with a fallback to rst2man) for the docs, I'd
like to hear them.