BUG: matplotlib.sphinxext.plot_directive uses old function-based API

[larsoner]

Working on scipy doc building I get this deprecation warning when running latest sphinx master:

/home/larsoner/python/sphinx/sphinx/util/docutils.py:271: RemovedInSphinx30Warning: function based directive support is now deprecated. Use class based directive instead.

Is anyone working on adding a new directive class that can be used instead of the directive function when calling app.add_directive?

I suspect it should be possible to try/except using a class instead of a function in setup(app) to maintain backward compatibility, so I'd try that first. Should I give this a shot, or is someone else working on it?