Provides a function for examining posterior MCMC samples
from a single chain using trace plots and density plots, and from
multiple chains by comparing posterior medians and credible intervals
from each chain. These plotting functions have a variety of options,
such as figure sizes, legends, parameters to plot, and saving plots to file.
Functions interface with the NIMBLE software package, see
de Valpine, Turek, Paciorek, Anderson-Bergman, Temple Lang and Bodik (2017)