+- removed Model::Init():
+ All initialization is now done in the default constructor in Model(). To
+ be compatible with the new API simply remove any calls to Model::Init().
+- removed constructor Body (mass, com, length, gyration_radii)
+ This constructor did some erroneous calculations to compute the real
+ radii of gyration. It was removed as the two remaining constructors are
+ properly tested and are more general.