Tutorials on RTD

[stonier]

Should be feasible to put them there as you should not need all the dependencies to build docs.

• Use a doc-requirements.txt and point rtd at that for installing sphinx and other sphinx modules.
• Use autodoc_mock_imports for any imports that aren't available at build time

[stonier]

The doc-requirements.txt works well, but unfortunately the autodoc_mock_imports doesn't. It barfs on submodules and similar (there is a few issues and PR's around this on the sphinx github project).