Support modern pseudo-random number generators from Numpy

[HDembinski]

General information:

• emcee version: 3.0.2

Problem description:

emcee does not seem to support the new Numpy random number generators.
https://numpy.org/doc/stable/reference/random/generator.html#numpy.random.Generator

I want to replace the Mersenne Twistor with the much better PCG generator. I tried setting .random_state on the EnsembleSampler and rstate0 on the run_mcmc call, but I always get "MT19937" when I call the random_state property on the output object.

[dfm]

The open pull request #376 adds this support but it's still a work in progress. You could follow that PR for updates or see if you could see how to push it over the line!