Major release of Matplotlib

This release completely overhauls the default style of the plots.

Highlights include:

 - 'viridis' is default color map instead of jet.
 - Modernized the default color cycle.
 - Many more functions respect the color cycle.
 - Line dash patterns scale with linewidth.
 - Change default font to DejaVu, now supports most western.
   alphabets (including Greek, Cyrillic and latin with diacritcs),
   math symbols and emoji out of the box.
 - Faster text rendering.
 - Improved auto-limits.
 - Ticks out and only on the right and bottom spines by default.
 - Improved auto-ticking, particularly for log scales and dates.
 - Improved image support (`imshow` respects scales and eliminated a
   class of artifacts).