Example plots for protocol documentation.

This PR extends the plotting routines to make a nicer labeled plot showing which part of the array is on which processor.

It adds the ability to specify a plot title, a filename to save to, and a colorbar 'legend' to identify which color is which processor. It also adds a new example file, which is intended to generate example plots for the protocol documentation.

The colorbar/legend is by far the most complicated part here.