Python threading comparison

[Dan Stromberg]

I put together a little python runtime comparison, with an embarallel,
cpu-heavy threading microbenchmark.

It turns out that the performance-oriented Python implementations, Pypy3
and Nuitka3, are both poor at threading, as is CPython of course.

On the plus side for CPython, adding cpu-heavy threads doesn't cause
performance to get significantly worse anymore.

The pleasant result is that Micropython threads pretty well!

There's a graph of the performance curves at:
https://stromberg.dnsalias.org/~strombrg/python-thread-comparison/