Bug fix release for 2.0.x series

This release includes bug fixes, documentation updates and one major change.

API

 - Do not clip the linewidth used for dash pattern scaling.  This is
   an API change, but is a major improvement.
 - Deprecate 'vega' color names in favor of 'tab'.

Bug Fixes

 - Hatching color follows edge color again.
 - Fixes a critical bug with masked images.
 - Improved high-dpi support for Qt5.
 - Log ticking no never skip minor ticks
 - Do not skip points surrounded by nan/inf in vector outputs.

Supported versions of Python

 - 2.7, 3.4, 3.5, 3.6
 - Patches to improve compatibility with pypy