Computes probability of the event \(p < p0\) (p0 is specified in [0, 1]) based
on posterior distribution of Beta-Binomial model with given parameters for prior Beta
distribution for all \(x = 0, 1, 2......n \) where n is the number of trials
References
[1] 2002 Gelman A, Carlin JB, Stern HS and Dunson DB
Bayesian Data Analysis, Chapman & Hall/CRC
[2] 2006 Ghosh M, Delampady M and Samanta T.
An introduction to Bayesian analysis: Theory and Methods. Springer, New York