v1.9.7.0

v1.9.7.0

New features:

1. rewrite statCovs method to get statistics and covariances for trees and datastes
2. add smattrix method to linalgt-objects
3. improve printout of marices
4. add mahalanobis distance
5. improve SVectorWithErrors
6. more improvements/fixes to weighting machinery

Backward incompatible:

Bug fixes:

1. fix a the bug/feature for statCovs for datasets
2. fix a bug/typo in asymmetric_kullback_leibler
3. fix missing factor 1/2 in kullback_leibler