DOC:Use monospace for --

The -- is rendering as an en dash on http://matplotlib.org/users/pyplot_tutorial.html

Maybe all strings should use monospace instead of single quotes?
DOC: Change all strings to ``'monospace'`` in quotes
DOC: Change strings to monospace
BUG: Fixed github stats retrieval

Currently urllib is used to retrieve a json file from Github, however
Github url used is not static url, urllib2 required to retrieve
information from Github.
add __enter__ and __exit__ to PdfPages
multipage pdf: show usage of with statement in example
Adding possibility to remove invisible lines and patches from relim
Remove dead RMS computation code
DOC: Add axes_api to documentation after the refactoring

Recently, axes was converted from a module to a package.
This adds axes_api to the doctree back.
`show-inheritance` was removed because it tells the user that
`Axes` `Bases: matplotlib.axes._base._AxesBase`
which is not that relevant I think.
This is mentioned in issue #1461
Adding test test_relim_visible_only
DOC: changed axes_api from automodule to autoclass

with automodule we had: `matplotlib.axes._axes.Axes`
while with autoclass we have `matplotlib.axes.Axes`

However, we must remember this documents only one class, so if
classes will be added to the module, they should be added
by hand.
Bug: alpha parameter was ignored when fill color is #000000
Merge pull request #2426 from mdboom/testing/remove-dead-rms-computation

Remove dead rms computation
Merge pull request #2319 from tacaswell/draw_idle_fix

fix draw_idle reference in  NavigationToolbar2
BUG: Fixed object type missmatch in SymLogNorm

Currently SymLogNorm accepts both linthresh and vmin, vmax with their
native dtype, meaning that the contents of one object cannot be updated
with another due to a mismatch of types.
Merge pull request #2242 from endolith/patch-3

DOC:Use monospace for --
Add webagg api docs
Document API change in hist
only show preferred usage of PdfPages in examples
show only preferred usage for PdfPages and use preferred pyplot import
style