DOC : improved `extent` of `imshow` doc

closes #990
slight edits to docs as suggested by @mdboom
BUG : instantiate fall-back writer

fixes #2651

If the a string is passed into save as `writer` the code tries to
look up a writer with that name and create it.  If a writer with that
name is not in the registry, it is replaced with the name of the first
writer that _is_ in the registry, but not an instance of that type.
BUGFIX:  This change fixes #2475, where contour labels added manually
produce ugly spikes in the contours.  The problem was that screen
coordinates were being passed as data coordinates when the contour was
split to add room for the label.

Incorporate my fix and miili's #2806 change
Fixes a bug in font family lookup.  Any font in the font alias
list (e.g. font.sans-serif) would be considered a perfect match whenever
the selected font alias is the first in the font.family list.  This
broke the priority ordering of font names.
Add test
Use assert_equal
No need to cast to floats with future division
DOC/ENH : get/set_size_inches

Added links between `get_size_inches` and `set_size_inches`

Added an `np.array` call to `get_size_inches` to return a copy of
the size, instead of a reference to the internal np.array.

Closes #2303
EXP : turn of clipping in spine example

Turn off clipping in the spine placement demos.

Closes #2795
(fix #2097) PGF: get fonts from fc-list, use builtin fonts for tests
TST : added test to exercise transform kwarg to `add_label_near`

This exercises with input in both display and data units.
BUG : Qt repaint workaround on windows

Added platform specific replacement of `update` with `repaint` in
`FigureCanvasQtAgg.draw` for windows.
DOC : minor tweaks to set/get_size_inches

 - better numpydoc style
 - added inch <-> cm conversion factor
Fix IPython detection.  Fix encoding error on Python 3
Remove _in_ipython
DOC : add link to `plt.subplots` from `Figure.add_subplot`
DOC : removed line about un-needed dependencies in Windows

We no longer bundle `dateutil` or `pyparsing`.
counterclock parameter for pie
ENH Added the origin option to `spy`

This option allows to place either the origin at the bottom of the axes, or at
the top.