mscBayesPost release 0.2.3

Adds support for sampler control lists allowing priors and tuning parameters
to be passed from gibbs_postscm() to internal Gibbs samplers.

Key changes:

• New control list for sampler priors and hyperparameters
• Support for configurable Sigma_gamma_prior
• Refactoring of Gibbs samplers to remove hard-coded prior values