Create simplifed workflow for posterior predictive checks.

[flyaflya]

Posterior predictive checks as advocated in

https://betanalpha.github.io/assets/case_studies/principled_bayesian_workflow.html#step_eight:_analyze_the_posterior_predictive_distribution

and

http://causact.updog.co/parameter-estimation.html#posterior-predictive-checks

can have an automated or easier workflow.