Use rtd sphinx theme outside of rtd.
Merge branch 'sdfits' into doc
New module autodoc template.
sphinx-rtd-theme in requirements.txt.
Requires more up-to-date sphinx.
Merge pull request #4 from kiyo-masui/doc

A variety of changes improving documentation and finally resolving Read-the-doc issues (see rtfd/readthedocs.org#732)