Address @aseth1 comment about StatesTrajectory doxygen.
Address @aseth1 comment about StatesTrajectory doxygen.

opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core