Docstring validation script: handle args/kwargs
This ensures that if you use `**kwargs` in the docstring Parameters, the validation script does not complain. 
But it does not yet check it is actually written like that.

Hello @jorisvandenbossche! Thanks for updating the PR.



Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on March 09, 2018 at 09:28 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20072?src=pr&el=h1) Report
> Merging [#20072](https://codecov.io/gh/pandas-dev/pandas/pull/20072?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/9119d076837dfcfe843726eb58cca4e449245562?src=pr&el=desc) will **increase** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20072/graphs/tree.svg?width=650&src=pr&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/20072?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #20072      +/-   ##
==========================================
+ Coverage   91.69%   91.72%   +0.02%     
==========================================
  Files         150      150              
  Lines       49112    49112              
==========================================
+ Hits        45035    45047      +12     
+ Misses       4077     4065      -12
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.1% <ø> (+0.02%)` | :arrow_up: |
| #single | `41.86% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20072?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/20072/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `66.81% <0%> (+1.73%)` | :arrow_up: |

------

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> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20072?src=pr&el=footer). Last update [9119d07...066fd2f](https://codecov.io/gh/pandas-dev/pandas/pull/20072?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 FYI, we use `**kwds` in some of the plotting docs. I haven't looked, but does that mess things up? We can / should just change those to `**kwargs`. lgtm. maybe we could/should run this in our lint.sh script? (or as an additional item in the CI). Gives much more deedback than the doc-build . Check is included for this in https://github.com/pandas-dev/pandas/pull/20061, so closing this