[WIP] Interface for Bayesian updating w/ conjugate priors

This is the start of work on an interface for Bayesian updating w/ conjugate priors. This implements the simplest cases involving Beta and Dirichlet priors. The general interface looks like:

    posterior(LikelihoodAsType, PriorAsDistribution, DataAsArray)

For example, this gives:

    posterior(Bernoulli, Beta(1, 1), [0, 0, 1, 1, 1, 0, 0, 0])