Prototype project for splitting pyplot in half

• Free software: 3-clause BSD license
• Documentation: https://matplotlib.github.io/mpl-gui.

This project is a prototype space for overhauling the GUI event loop management tools that Matplotlib provides in pyplot.

The pyplot module current serves two critical, but unrelated functions:

1. provide a state-full implicit API that rhymes / was inspired by MATLAB
2. provide the management of interaction between Matplotlib and the GUI event loop

While it can be very convenient when working at the prompt, the state-full API can lead to brittle code that depends on the global state in confusing ways, particularly when used in library code. On the other hand, matplotlib.pyplot does a very good job of hiding from the user the fact that they are developing a GUI application and handling, along with IPython, many of the details involved in running a GUI application in parallel with Python.