REL: v3.0.2

This is the second bug-fix release for the v3.0 series.

 - Un-breaks basemap which was broken by partially restoring
   private APIs for cartopy.
 - Fixes bug in warning code when used in an embedded context.
 - Fixes crash when using Tk and closing the first open window before showing it
 - Many documentation improvements.
 - Restore a corner case on ColorBar tick usage.
 - Change the default behavior of `matplotlib.use` to silently allow
   more 'safe' switching after auto-discovery, but before starting an event loop.
 - Improvements to bounding box calculations.
 - Provide the correct length for RcParams instances.

Author: tacaswell