matplotlib Code

Rework the nan-handling/clipping/quantizing/simplification
framework so each is an independent part of a pipeline.
Expose the C++-implementation of all of this so it can be
used from all Python backends. Add rcParam
"path.simplify_threshold" to control the threshold of
similarity below which vertices will be removed.

removed extraneous savefig calls from examples

added more examples to backend driver

Make scale colors match line colors in two_scales.py

added rc param axes.unicode_minus

removed deprecated example

moved fill_between to axes/pyplot method

updated api for fill_between_where and span_where

renamed fill where examples

generalized fill between poly collection