Merge pull request #2159 from mdboom/misc/docstring-inheritance

Automatically inherit docstrings from base classes
Don't generate the config file any longer, just keep it in the repo and
copy it over.
Add a test.
Remove save functionality from config
First pass at moving around all of the configuration options.  Tests passing.
Don't warn on import
Notate the version at which configuration items were renamed.
Fix more warnings on import.
Minor docstring improvements.
Make configuration items show up in docs
Update config doc pages.
Document configuration changes.
Reorganize astropy.cfg based on general categories in docs.
Correct APE5 -> APE3
Test ScienceStateAlias.
Some Sphinx doc fixes.