First git documentation build.

Hi,

I've managed to get a documentation build working from git. I haven't
fixed anything yet, and when I ran inspect it was without running 'b2
headers' so all the header links are broken. This could be easily
fixed by running 'b2 headers' but I'd rather link to the modules'
headers. I'm not sure if that will be possible, but please don't worry
because these is an easy fix to fall back on.

The inspect report is here:

http://boost.cowic.de/rc/docs-inspect-master.html

You can also grab the documentation from:

http://boost.cowic.de/rc/boost-master-docs.7z

Remember that doesn't include things like css files so it needs to
exported inside a boost checkout to be fully visible. And that this is
just the first build, I've only been dealing with mechanics of running
it.

Daniel