rename `mpl_gui.show`

[tacaswell]

The name is a good one, but mpl_gui.show (which requires a list of Figures to be passed) has a very different API than FigureRegistry.show (and mpl_gui.registry.show) and matplotlib.pyplot.show (to which you may not pass a list of Figures).

The current leading contender is display

[jklymak]

Is it the same idea as "draw" or does it do more than just draw the listed figures?

[tacaswell]

It does the actual creation of the GUI elements, puts them on screen, and then spins the event loop. I went with display in #17.