How should the docs be versioned?

[Katherine Marsden]

The docs say version 0.3.0 which I think should at least be updated 
0.4.0 but maybe 0.5.0 prerelease if we are going to be working on master 
to update them with current development work.

Once we have a release, will we be providing multiple versions of the 
doc on the website?  If so, how will this work?

Thanks

Kathey