MCMC model composition to sample variables for changing model size in BMA
[vin,vout] = mc3_g(vin,vout,nvmax)
* vin = vector of variable numbers for variables included in the model
* vout = vector of variable numbers for variables excluded from the model
* nvmax = max # of variable allowed in each model
* vin = vector of variable numbers in the new model
* vout = vector of variable numbers excluded from the new model