Updates to user manual

[Dirk Hohndel]

On Tue, 2013-12-03 at 22:02 +0200, Willem Ferguson wrote:
> Updates to user-manual. I added two more technical references (including 
> Erik Baker) to the end of the section on dive profiles, dealing with 
> gradient actors. Is this ok? Otherwise the GF settings hang in the air. 
> I put the reference texts in a directory called references.

I don't think we have a license that allows us to include the PDF in our
sources - I would much rather have a link to it somewhere.

So I'll drop that from your patch.

/D