improve documentation surrounding optional deps
kill some automodapi bugs
more doc tweaking and warning removal
more error crushing
back to the astropy database rst
more database patching
fix database table docs
remove database inheritance diagrams
add pytest to doc requirements.txt
tweak optional requirements
remove database.Database attrs and methods from primary docstring
Fix revert in GenericMap docstring
Merge pull request #724 from Cadair/doc_sprint_2

improve documentation surrounding optional deps