DOC: Reorganize plotting.rst

[TomAugspurger]

With the recent additions of hexbin, area, table, and pie charts (I may be forgetting some), the visualization docs are getting a bit long. I'll reorganize things to hopefully be a bit clearer.

I'll also mention things like seaborn, ggplot, mpld3, vincent, bearcart, and maybe remove the note that we plan to add more integration with maptlotlib.

• link to matplotlib functions
• all calls using random should be seeded so people can reproduce

[TomAugspurger]

Is anyone familiar with sphinx's intersphinx? I'm trying to link to the matplotlib docs. I see that we have it setup for statsmodels and python.org docs, but do we use it in the docs? @hayd you get blamed for touching that section of the sphinx conf.py, but I think that was part of a pep8 cleanup.

[TomAugspurger]

Nevermind, I think I have it working. I'll try to benchmark if this increase the build time of the docs.

[jreback]

I think maybe just use and maybe mention visibly

import pandas as pd
import numpy as np
np.random.seed(1234)

(even though it takes up space)

[hayd]

There was a pep8 bug (with sphinx's hashbang syntax, hope that didn't screw anything up)...

[jorisvandenbossche]

@TomAugspurger about intersphinx, it is also added in another PR: https://github.com/pydata/pandas/pull/6976/files (not merged yet). There another link is used, but I don't know which is the correct one, you should just test it if it works.