added option to MCMCspec for multivariate nodes as scalars
added option to MCMCspec for multivariate nodes as scalars

NLMichaud/nimble,NLMichaud/nimble,nimble-dev/nimble,nxdao2000/nimble,nimble-dev/nimble,nxdao2000/nimble,nimble-dev/nimble,nimble-dev/nimble,nxdao2000/nimble,nimble-dev/nimble,nxdao2000/nimble,NLMichaud/nimble,NLMichaud/nimble