DOC: update numpydoc to current master (commit 223df02530)

This PR updates our local copy of numpydoc to latest upstream version (I just fully copied over that version, only left out setup.py and manifest.in). This would be a solution to the numpydoc part of issue #5221.

The intent would then be, from now on, to not touch this code, apart of pulling an updated version from numpydoc upstream from time to time. If we want to make a change, also send it upstreams to not let the two versions diverge.

**Other options** to solve this issue would be to just add numpydoc as a requirement for the doc building and removing out local option, or to add it as a git submodule. I am slightly in favor of removing our local copy, but I understood from previous comments it would be better to not have more build dependencies (and it would also tie us to a specific version).

I did build the docs with this and all seems OK. From looking at the history, I think only py3compat changes are done to these files after the initial import from Wes (@jtratner, @cpcloud you are the ones who touched these files, do you remember if you did something else than py3compat issues?)