Create an object of type "GaussianNIW", which represents the Gaussian-Normal-Inverse-Wishart (Gaussian-NIW) conjugate structure:
theta|gamma ~ NIW(gamma)
x|theta ~ Gaussian(theta)
where theta = (mu,Sigma) is the Gaussian parameter, gamma = (m,k,v,S) is the Normal-Inverse-Wishart(NIW) parameter.
This object will be used as a place for recording and accumulating information in the related inference/sampling functions such as posterior(), posteriorDiscard(), MAP() and so on.