The first release of the v2.2 LTS series and the last version of
Matplotlib to support python2.  There will be bug-fix release for this
series until 2020.

This release includes new features including:

 - An experimental constrained layout manager
 - Color blind friendly color map (cividis) and color cycle
   (tableau-colorblind10)
 - native support for numpy.datetime64 types
 - animated gif writing via pillow
 - TkAgg now works with pypy
 - cairo based backends for Qt, Tk, and WX

There are several API changes in this release:

 - To support the constrained layout Matplotlib has a new required
   dependency (kiwisolver).
 - The `matplotlib.finance` module has been removed, development has
   moved to a stand-alone project.