DOC: Add plotting examples and fix broken examples
This PR improves the `pandas.plotting._misc.py` module docs by:
1. Adding example plots where they were missing from docstrings.
2. Fixing examples that were not formatted to render with
```
.. plot::
    :context: close-figs
```
3. Simplifying the syntax of some oddly-written examples.

In some cases, I replicated the examples found in the [User Guide](https://pandas.pydata.org/pandas-docs/stable/user_guide/visualization.html#plotting-tools).
Hello @deppen8! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:



There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-05-05 21:05:27 UTC Thanks @deppen8, cool stuff. Did you render the website to see that everything is looking as expected?

@jorisvandenbossche, may be you want to have a look here. @datapythonista, I built the docs locally and nothing looked out of order.

@jorisvandenbossche I found this advice which suggested using random seeds.

https://pandas.pydata.org/docs/development/contributing_docstring.html#tips-for-getting-your-examples-pass-the-doctests

In the case of the lag plot, it has an added benefit of keeping the demo data above zero, which probably matches most use cases better. > I found this advice which suggested using random seeds.

Ah, yes, but that's only to get doctests passing where eg a number is shown in the output, while here the plots are not actually checked.

For the lag plot that sounds like a good reason, for the others I would maybe remove it again, if we don't do that elsewhere > For the lag plot that sounds like a good reason, for the others I would maybe remove it again, if we don't do that elsewhere

Done! Thanks @deppen8 !