Adding Wishart and Inverse Wishart pdfs and random deviates

This introduces two new matrix variate distributions, the Wishart and Inverse Wishart, which are important as conjugate priors for precision/covariance matrices.  The RNGs and pdf calculations have been tested against their equivalents in R.  The thing I'm not totally sure about is how you want the type hierarchy to work for matrix variate distributions, so feel free to suggest changes there.