Added log of mutivaraiate gamma function and log determinant functionality on the C++ side.
Added pool-function for combining a list of scatter matrices into the pooled estimate.
Minor clean-up.
Exported log-determinant and log multivariate gamma function.
Added Graphical Random Effects Model (GREM) fitting procedures and workhorse functions.
Clean-up by removed "old" version and use the fastest available.
Export core GREM user functions.
Fixed wrong function call.
Fixed issues in fit.grem.moment.
Changed order of arguments in fit.grem.MLE and fit.grem.moment.
They are also no longer exported.
 Minor clean-up.