MAINT Backporting of #7995.

* Update documentation of stem

changed here: matplotlib@d68662a

* Update vlines example with axes wide lines.

* Clean up BoundaryNorm docstring

* Document what happens when ncolors > bins

* BoundaryNorm docstring clarification

* BoundaryNorm docstring formatting

* Added set_xlim and set_ylim check for non-finite limit values

* FIX: masked images with interpolation

When determining which pixels to mask in the resampled image, if _any_
contribution to final value comes from a masked pixel, mask the
result.

Due to Agg special-casing the meaning of the alpha channel,
the interpolation for the mask channel needs to be done separately.
This is probably a template for doing the over/under separately.

print out exact hash on travis

* Cleaned up invalid axis limit warning text

* FIX tick label alignment can now be specified

This patch adds two new rcParams allowing to set label alignment. The sole
reason for the existance of these new parameters is to allow user to reset the
style to before 2.0 for testing purposes. More specifically, ytick horizontal
alignement was changed in a non backward compatible way. xtick vertical
alignement was added for API consistency.

closes matplotlib#7905

* MAINT created a new private _classic_test stylesheet

This allows the public classic stylesheet to be 'more' backward compatible

* FIX small nitpicks

* Template-ize visual_tests.py.

* Pass missing variable to format string.

* Simplify dictionary access in visual_tests.py.

* PEP8 visual_tests.py.

* Sort results in visual test HTML.

This makes the result a bit more reproducable and comparable.

* Don't start a browser for visual tests on CI.

Travis may or may not have a browser installed, but AppVeyor definitely
does, so this saves a tiny bit of processing power per run.

* Move visual_tests into tools.

* Add tools directory to pep8.

* pgf: Fix invalid arguments passed to pdftocairo.

This breaks saving PNG when using the PGF backend.

Fixes matplotlib#8121.

* MAINT Backporting of matplotlib#7995.

Set sticky_edges correctly for negative height bar().

* Small docstring fixes

* merge fill_demo and fill_demo_features

* move imports below title

* Merge docstring coherent

* Plot errorbars if fmt=='none'

* Add test for fmt=='none'

* Fix small spelling mistake

* Check plotted bars are color C0

* Add cleanup to new test

* Simplify multicolored_line example

* Move multicolored_line example

* Small fixes

* Put boundarynorm example back in

* Add autoclass entry for Artist API doc.

Adding an autoclass entry in the Artist API ensures that that class
appears in the intersphinx `build/html/object.inv`, as can be checked by
```
"matplotlib.artist.Artist" in (
    sphinx.ext.intersphinx.read_inventory(
        open("build/html/objects.inv", "rb"), None, lambda *args: None)[
            "py:class"])
```
(now returns True).

This allows other projects to link to that class in their docs using
```
`Artist` <matplotlib.artist.Artist>
```

This possibility used to be present, but disappeared when the Artist API
doc got refactored.  (Other classes that appear in the API docs are fine
as they already use autoclass.)

* Merge pull request matplotlib#8171 from afvincent/typo_eventplot_docstring

DOC: Fix small typos in 'eventplot' docstring

* Fix layout of spectrum_demo.py

* Beautified spectrum_demo.py a little more.

* Added plot titles to spectrum_demo.py

* Correct theta values when drawing a non-circular ellipse

Make arcs work with units

Add api change not for elliptical notes

Add background ellipse and extra line to test

Remove pdf and svg tests for arc angles

* Fix small typo in api change

* add gitter link in README

* add a line to README that explains use of gitter

* Fixes matplotlib#8141
Validators for dashed linestyles now allow None as an allowed value along with floats through optional `allow_none` kwarg in validate_nseq_float. Other validators that use validate_nseq_float arent affected

* Replace second instance of gitter badge with a link

* TST: Enable cache directories on AppVeyor.

* Use secure links to FreeType tarballs.

* Try harder to cache FreeType tarball on Python 2.

* TST: Always delete extra cache files on Travis.

Note, we don't need to do this on AppVeyor because the cache directories
are different.

* add parameter and test

* implemented label rotation

* pep8 fix

* DOC moved autowarp_demo to sphinx-gallery compatible docstring

* DOC spines example are now sphinx-gallery compliant

* DOC all tick labels examples are now sphinx-gallery compatible

* DOC moved text_demo_fontdict to sphinx-gallery compatible docstring

* TST: skip fc-list related tests if not installed

* DOC FIX removed a blank line from an example

* DOC moving showcase examples to sphinx-gallery

* Plural of axis is axes

* add early check for dot binary (from graphviz) when building the doc

* Clarify segment array shape

* Make ginput dostring into a numpydocstring

Small fixes

Add default value for npoints

Suggested changes to ginput docstring

Better description of ginput return

Put summary line by itself at the top

Add in missing full stops

* Implement Path.intersects_bbox in C++ to speed up legend positioning.

* DOC removed/added blankspace

* DOC fixe small typos and blank lines

* DOC capitalized firefox

* renamed flag to 'rotatelabels'; fix vertical alignment

* Update spines_demo.py

* MEP12 alignment_test

* Move alignment_test example

* MEP12 and simplify ganged_plots example

* Move ganged plots example

* pep8 fix

* added headers

* added/fixed headers

* DOC removed redundant call to plt.show()

* DOC added docstring to vline-hline example.

* fix gitter badge

* Set subplot spacing to zero

* Clean up description wording

* fix rst markup

* Fix pep8 violation

* Fix example description phrasing

* Remove image with non-free color calibration profile

The example that used to use this image was remove already in commit 9692c31.

This closes matplotlib#8034.

* MAINT Backporting of matplotlib#8241: remove possible non-free image

* Ignore invisible axes in computing tight_layout.

* combining and updating 2d hist examples

* consolidating histogram examples and moving to SG folder

* Memoize parse_fontconfig_pattern; speeds up test suite by ~1min.

On my laptop this patch drops the duration of the test suite from 604s
to 554s (with the inkscape patch on as well).

* addressing small change comments

* Contouring 1x1 array (issue 8197)

* another attempt; add a test

* Set __name__ for list validators in rcsetup.

This avoids having many validators all named `f`, which makes profiling
a bit difficult (it appears that repeated validation of rcparams when
resetting the style at the beginning of each test instance contributes
quite a bit to the total test time).  Instead, the list validator
based on scalar validator function `validate_foo` is now `__name__`d
`validate_foolist`, and the list validator based on scalar validator
class `ValidateFoo` is now `__name__`d `ValidateFooList`.

* TST: fail on missing baseline file

* re-add conditional check.

* DOC moved spines examples sphinx-gallery

* Use sys.executable -msphinx instead of sphinx-build.

* More robust type checking in '_validate_linestyle', on both Py2 and Py3

* tests now depend on python version to check cases with bytes args

* DOC changes in travis's build environment

* DOC removed duplicate appveyor py3.5 environment

* CI: travis runs documentation build and mac osx only on merge with master

* MAINT remove py.test from our travis build

* FIX appveyor doesn't need option USE_PYTEST anymore

* append test images.

* removed obsolete license.py file

* DOC moved changelog to the documentation

* DOC fix broken links

* MAINT moved some maintenance and helper python scripts to tools/

* FIX path in boilerplate.py

* Small header comment fixes

* Removes OldScalarFormatter

* Renaming file to scalarformatter_demo.py

* Renaming to plot_scalarformatter.py

* Adds title and description

* changing name in backend_driver.py

* Inkscape shell mode.

* Fix minimum sphinx version in doc-requirements.txt.

* Correcting typos and moving file to ticks and spines

* STY: fix whitespace in the tests

* Remove executable bit from examples and headers.

The vast majority of examples do not have the executable bit set, so
just make everything consistent.

Also remove `#!/usr/bin/env python` where appropriate.

* DOC shapes and collections is fully SG compatible

* Use neutral pronoun in docs.