ADD: new track message, Entity class and Position class

libs/eigen/doc/snippets/HessenbergDecomposition_matrixH.cpp

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+Matrix4f A = MatrixXf::Random(4,4);
+cout << "Here is a random 4x4 matrix:" << endl << A << endl;
+HessenbergDecomposition<MatrixXf> hessOfA(A);
+MatrixXf H = hessOfA.matrixH();
+cout << "The Hessenberg matrix H is:" << endl << H << endl;
+MatrixXf Q = hessOfA.matrixQ();
+cout << "The orthogonal matrix Q is:" << endl << Q << endl;
+cout << "Q H Q^T is:" << endl << Q * H * Q.transpose() << endl;