HMC, RWMH sampling methods tutorial

[yebai]

We might want to add a comparison oriented tutorial for various sampling algorithms at some point. Two previous tutorials that I find relevant are

• https://github.com/mlss-2019/tutorials/blob/master/mcmc/3%20-%20hamiltonian_monte_carlo.py
• https://github.com/salilab/hmc/blob/master/examples/notebooks/basic_usage.ipynb

[cpfiffer]

Good ones, I'll stick it on the to-do pile.