The first release of the v3.1 series
This version of Matplotlib support Python 3.6+
Highlights of this release include:
- A helper method for scatter legends
- Secondary axis support (ex, degrees and radians)
- A concise date formatter
- No longer requires a framework build of Python to use OSX backend
- Major and minor ticks will no longer collide by default
- A progress callback for animations
- mplot3D is always registered
- deprecated mlab functions have been removed
- Many function calls have become stricter about invalid or ignored input
