Add wiki installation guide to main docs.

Hi,

I really should have done this a long time ago, but if no one
disagrees I'm going to add a new installation guide based on the wiki,
and replace the old installation guides from boostbook and quickbook
with links. I've put an initial version up at:

http://www.calamity.org.uk/doc-tools/

It isn't finished yet. At the very least, I'm going to have a look
through the boostbook and quickbook documentation, to make sure that
nothing is lost and add anything useful contained within them. I'll
probably add an 'alternative installation' section which mentions the
boostbook auto-installation script and maybe some other things.
There's also some 'TODO's in there.

The repo is on github at:

https://github.com/danieljames/boost-doc-tools

If there's any changes you'd like to suggest you should be able to
edit it and submit pull requests through the web interface. If you go
to the appropriate qbk file, there should be an 'edit' button at the
top right of the source code. You'll need to be logged in.

Hopefully this should be in the next release. And from there we can
add further user information. Probably very slowly, but that's the way
of things.

Daniel