Reorganized SimpleDemo a little bit.
Moved top hypotheses/samples methods from VectorSummary to MCMCSummary.
Added gridplot to VectorSummary -- when working this will allow us to see what happens with MCMC much easier.
Working more on gridplot.
Added MixtureGrammarHypothesis so we can do GrammarHypothesis inference with a mixture model (as in Josh's thesis).