Some minor fixes

Some minor docs fixes while I was browsing through the code ...

There's a few other things that could be improved, but I don't have the time to do it this week:
* There's no Sphinx search field when building the docs locally with `python setup.py build_sphinx`. Maybe adopt the Astropy docs template or fix this some other way?
* Astropy and the package template use `docs/api` as an output folder to store the auto-generated API docs. You put hand-written `rst` files there, which I first deleted by accident trying to produce a clean Sphinx build. Maybe change this?