REL: v2.0.0b1

First beta release of v2.0.0

This previews the new default style and many bug-fixes.  A full list of
the style changes will be collected for the final release.

In addition to the style change this release includes:
 - overhaul of font handling/text rendering to be faster and clearer
 - many new rcParams
 - Agg based OSX backend
 - optionally deterministic SVGs
 - complete re-write of image handling code
 - simplified color conversion
 - specify colors in the global property cycle via `'C0'`,
   `'C1'`... `'C9'`
 - use the global property cycle more places (bar, stem, scatter)

There is a 'classic' style sheet which reproduces the 1.Y defaults:

   import matplotlib.style as mstyle
   mstyle.use('classic')