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
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
colors: Replace docstring ''' with """
test_colors: Fix typo
colors: Add power-law normalization
power_norm_demo: Initial commit
hist2d: Add a note mentioning PowerNorm
Merge pull request #2844 from tacaswell/qt_win_specialcase

BUG : Qt repaint workaround on windows
Radius fix in _path.cpp

Updated the points_in_path method to allow negative radii as is implied by the documentation.
BUG: Removes iteration over locals (no-no) in mathtext
Added test for negative radius in Path.contains_points
Added point which is inside the unit circle but not inside a circle of radius 0.5
BUG: Fixed bug in handling drawing bitmap images accounting for the device scaling
DOC : added missing doc changes from #2844
Merge pull request #2939 from cimarronm/macosx_device_scale

Fixes a bug in drawing bitmap images in the macosx backend for handling device scaling
Merge pull request #2915 from simongibbons/master

Consistency of the radius argument for Path.points_in_path
Merge pull request #2926 from cimarronm/mathtext_remove_locals_iter

BUG: Removes iteration over locals (no-no) in mathtext
PEP8 : add missing line to un-break build
Fixed issues with errorbar limits