Support documentation versions

[huntc]

We now need a 1.0 branch of the ConductR documentation. Consequently project-doc should be set up to:

• permit selection of documentation versions; and
• source the doco from the appropriate branches.

[huntc]

Fixed by #42

I'm leaving out the selection ability given that we're not actually ready to release 1.1 of course. We can easily address selection given the work that has now been done.