Record process to produce nicely styled plots

[mrocklin]

@pentschev is able to produce nicely styled plots from the output of these tests. It would be good to record this process somewhere so that others could take on this work.

From my understanding reading various slack messages one needs to pass the following flag to save a JSON file.

--benchmark-json=benchmark_result.json

And then use the process in this notebook:

https://github.com/pentschev/pybench/blob/master/examples/plot_array_example.ipynb

Ideally we would convert that notebook to a script or Python function that could be run without invoking Jupyter, then we would write down a few lines that someone could copy-paste into a terminal somewhere into the README.

I think that it would be great if someone other than @pentschev could clean this up. I suspect that this project would benefit from having another pair of eyes.