Pep8ify examples

This PR converts the animation, api and axes_grid examples.

(Retry of #3182/#3183)

I addressed @ianthomas23' comments from #3183
Ah, yes. So, a quick read through that file, it seems to me that we don't
pep8 test the example files at all, I think? Should we?


On Thu, Aug 28, 2014 at 9:52 AM, Thomas Hisch <notifications@github.com>
wrote:

> In examples/api/collections_demo.py:
>
> > @@ -27,10 +27,10 @@
> >
> >  # Make some spirals
> >  r = np.array(range(nverts))
> > -theta = np.array(range(nverts)) * (2*np.pi)/(nverts-1)
> > +theta = np.array(range(nverts))*(2*np.pi)/(nverts - 1)
>
> @WeatherGod <https://github.com/WeatherGod> are you referring to the
> blacklist in the test_coding_standards.py file?
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/matplotlib/matplotlib/pull/3425/files#r16839843>.
>