Patching the docs

[dhuppenkothen]

I've been reading the documentation (thank you! this is a great package!), and found some minor formatting issues with the docs:

• some sections in a couple of notebooks used "#" to define a section headline, which led to those section headlines appearing in the documentation sidebar. For example, there's an entry in the sidebar called "defining the likelihood", but it leads to a section in a specific example notebook. Since most entries in the sidebar correspond to titles of notebooks, I figured these probably should not be there
• The Gaussian Processes with Outliers tutorial seems to exist twice, but is actually two different things, so I disambiguated those
• The Introductory Example doesn't actually appear in the documentation, because it didn't have a title in the notebook, so I gave it one and made sure it appears at the top of the sidebar.

[Joshuaalbert]

Thanks @dhuppenkothen for the contribution. LGTM

[dhuppenkothen]

Just FYI: I just realised I don't think the introductory example actually runs (I think it might be using an old syntax? I can try to fix that here (in which case hold off from merging) or open a new issue/PR?

[Joshuaalbert]

I think all the tutorials need to be reworked over, made much better in general, with more description and variation of the types of things that can be done with JAXNS. Let me know if you have a syntax problem.

Also, to run the notebooks you can run the nbconvert_all.sh script in the examples dir. It might take a few minutes to complete.