Add separated impl of MatricCovarianceFunction
Add separated impl of ExponentialMatrixCovarianceFunction
Add separated impl of GenericMatrixCovarianceFunction
Add make rules for new MatrixCovarianceFunction files
Merge remote-tracking branch 'origin/sep_impl_matrixcov' into dev

Conflicts:
	inc/queso/Makefile.am
	src/Makefile.am