Figure out communication to github.io from readthedocs.org

[darribas]

If the user goes to pysal.github.io, it is straightforward to access the documentation in pysal.readthedocs.org However, if the user wants to go back to the (up to date) home page in pysal.github.io from pysal.readthedocs.org, there is currently no link. This could involve setting up a way so that docs generated by sphinx pointed to pysal.github.io in certain pages (home, upcoming events, news and funding). Alternatively, these pages could be removed from sphinx and kept only under pysal.github.io

[sjsrey]

I agree we need a way to move the user back and forth.
I guess once we decide what goes here, and what is on the documentation site it is a matter of setting up the links appropriately. For a way to get back to the gallery from the rtd site see pysal/pysal#516