Add reversible jump MCMC

[rlouf]

Reversible Jump MCMC algorithms are a generalization of the Rosenbluth-Metropolis-Hastings algorithm for when the target density does not have a fixed number of dimensions. Since aesara can handle variables of varying dimensions we should be able to implement such algorithms in aehmc.

As a motivating example we could use the coal-mining disaster datasets and let the number of change points be a Poisson-distributed as in the reference below.

References

https://www2.stat.duke.edu/~scs/Courses/Stat376/Papers/TransdimMCMC/GreenRevJump.1995.pdf

[zoj613]

I thought this was a PR. I was going to say you're on fire this week