Translate nonlinear state-space model from BUGS to Stan and diagnose potential problems in the posterior.

Model from two papers:

- Meyer, Renate and Russell B. Millar. 1999. BUGs in Bayesian Stock assessments.
*Canadian Journal of Fisheries and Aquatic Sciences*. 56:1078-1086. - Millar, Russell B. and Renate Meyer. 2000. Non-linear state space modelling of fisheries biomass dynamics by using Metropolis-Hastings within-Gibbs sampling.
*Applied Statistics*. 49, Part 3: 327-342.