BUG: Wfpt.random is fixed
CHG: chg/add quantiles methods for wfpt, and fix _plot_posterior_quantiles_node
MIN: minor correcitons
Merge pull request #17 from hddm-devs/ppq_fix

CHG: chg/add quantiles methods for wfpt, and fix _plot_posterior_quantil...
Merge branch 'master' into develop