I have the most basic implementation of the mixture model working.
Updated examplemix.m.
Added BETAMEANMIX function for easily computing the mean for the
mixture model.
Updated the preliminary steps for VARBVSMIX.
Updated BETAVARMIX.
Updated computation of variational lower bound for mixture model.
Fixed up VARBVSMIX a bit.
Fixed up update for sigma in VARBVSMIX.