Add support for autoexception directive

[andy-maier]

The Sphinx autodoc extension supports a directive autoexception (https://documentation.help/Sphinx/autodoc.html#directive-autoexception).

Specifying :autosummary: on the autoexception directive fails:

.../docs/client/exceptions.rst:49: WARNING: An option to autoexception is either unknown or has an invalid value: 'autosummary'

For consistency, it would be great to enable its use. I believe the autoexception directive behaves pretty much the same as the autoclass directive, but I did not dig deep into this. The autodoc documentation is not very specific about it, unfortunately.