Moved python files from doc/pyplots to examples folder

[wgma00]

Completed the first two changes specified in #7390 . When I was looking through the pyplots files with grep I didn't spot any places where the stdlib random module was used in stead of the numpy.random module.

[tacaswell]

modulo the docs building cleanly on travis

[NelleV]

That's great!
Thank you for doing this work.

[QuLogic]

I wonder if this and the section above is relevant any more? I don't see either README or make.py in the original doc/pyplots.

[NelleV]

The failing tests are pep8 related error, which we probably don't want to fix in this PR…
If we merge, what's going to happen? How are the pep8 tests ran?

[QuLogic]

You can add those files to the list near the end of lib/matplotlib/tests/test_coding_standards.py to ignore the pep8 warnings for now.

[efiring]

Strangely, the pep8 checker doesn't ignore the excluded files, it checks to make sure they need to be excluded!

ValueError: Some exclude patterns were unnecessary as the files they pointed to either passed the PEP8 tests or do not point to a file:
  */pyplots/pyplot_scales.py
  */pyplots/pyplot_text.py
  */pyplots/pyplot_three.py
  */pyplots/whats_new_99_mplot3d.py

[NelleV]

The strategy implemented on #7403 which runs flake8 on diffs fixes the issue we have on this PR.

Currently, there is a test that ensures that blacklisted files need to be blacklisted. Hence the new failure.

[NelleV]

Thanks @wgma00 for the patch!

Cherry-pick in 2.0 with 263e675

[tacaswell]

Complaining that an excluded file passes is a feature of the system to (slowly) ratchet our way to PEP8 compliance (so we do not accidentally fix a file and then break it again).