Support "Keyword Arguments" sections in Google-style docstrings

[pawamoy]

Is your feature request related to a problem? Please describe.
Keyword sections is useful to document the possible contents of **kwargs. Without it, users must write keyword arguments documentation in the Arguments section, under the **kwargs parameter, using plain Markdown, therefore not benefiting from the table template.

Describe the solution you'd like
Support keyword arguments section in the google style parser.

Describe alternatives you've considered
As mentioned previously, an alternative is to document kwargs in the Arguments section, but this is a bit tedious to do it right.

Additional context
Only the Google-style parser is concerned by this feature request. Other issues will be needed for the other parsers, if needed.
Originally asked on mkdocstrings: mkdocstrings/mkdocstrings#205

[HacKanCuBa]

Adding for reference that napoleon supports it: https://sphinxcontrib-napoleon.readthedocs.io/en/latest/index.html#docstring-sections

[pawamoy]

Thanks ☺️

Note that the feature request is accepted, we just need time from the maintainers (me, probably) or a PR 😛

[HacKanCuBa]

hahaha I see what you did there 👯

Anyway, I hacked a PR, will push soon.