Use rtd sphinx theme outside of rtd.
Merge branch 'sdfits' into doc
sphinx-rtd-theme in requirements.txt.
Requires more up-to-date sphinx.
Revert "Got rid of module.rst.  Does nothing."

This reverts commit 3f75ad21555001c716be6c42b17bc73929a70f99.
Merge pull request #8 from kiyo-masui/doc

Gets readthedocs to work.