Include full attribute docstrings in autosummary - #268

This seems fine, except for two things:

• Can you move the "Attribute Documentation" after the "Methods Summary" section? That way the summaries all come before the actual documentation.
• I get 4 warnings that now appear when I build the docs. I'll see about fixing them and I'll submit a PR to your branch

See mdboom#4 for a fix for 3 of the 4 warnings that result. The last one is more complicated and I'm fine with merging this and fixing that separately.

Changed the ordering of the elements.

I also fixed a minor problem whereby if a class had no methods empty "Methods Summary" and "Methods Documentation" sections were still being created.

@mdboom - are you going to merge mdboom#4 into this (that's on your branch here, so it would be included in this PR) or should we merge this and have me apply that separately?

(Other than that, I think this is good to merge)

I'm just waiting for @iguananaut to comment on it as it affects the io.fits documentation, but I suspect the likelihood of it being a problem is low.

Looks fine to me.
This reminds me that at some point I need to go through pyfits' docstrings and make links out of all the ticket references.

I'll go ahead and merge this, and try to solve the final remaining warning separately.