I just tested and used this package. I noticed that the Gibbs sampler does not necessarily start in a feasible point (within the polygon). For large-dimensional problems, this can make the chance of arriving in the feasible space by random sampling extremely low.
I made a small modification to the code by using the constrained maximum likelihood solution as the first sample. This helps to avoid this situation.
Otherwise, I think this is a great piece of code. Thanks for sharing.