Plya Tree Type Models // Fits Bayesian nonparametric models based on Plya tree processes, including adaptive Plya trees, Markov adaptive Plya trees, optional Plya trees, and their conditional-density counterparts. Methods are described in Ma (2017) doi:10.1214/16-BA1021, Ma (2017) doi:10.1214/17-EJS1254, and Wong and Ma (2010) doi:10.1214/09-AOS755.