Fix readthedocs fixes 438

[peterbe]

I did this:

$ mv docs /tmp/
$ sphinx-autostart 
(answer no to almost all questions)
$ cd docs
$ cp /tmp/docs/*.rst /tmp/docs/run.sh /tmp/docs/Dockerfile .
$ make html

Then I made it so that any warnings are turned into errors and I changed the default theme (alabaster) to the old (sphinx_rtd_theme) theme.
I also, copied the old theme_overrides.css as before but I have no idea what it does.

Not looking for a thorough review. I just want to get the ReadTheDocs to work again. And by using the sphinx-autostart we get something much simpler and closer to the default.

[peterbe]

r=me