fixing bug in resampling.  needed to compute scaled statistics using the precisions.  as an added benefit, this avoids memory copies, and should make the code a bit faster.

adding a robust regression class with multivariate-t distributed noise.  no sampling of degrees of freedom yet.

ensure nu is int when sampling inverse wishart

Diag regression

updating DiagonalRegression to accept sufficient statistics of the same form as the standard Regression class