ADD: new track message, Entity class and Position class

libs/eigen/doc/snippets/MatrixBase_cwiseNotEqual.cpp

@@ -0,0 +1,7 @@
+MatrixXi m(2,2);
+m << 1, 0,
+     1, 1;
+cout << "Comparing m with identity matrix:" << endl;
+cout << m.cwiseNotEqual(MatrixXi::Identity(2,2)) << endl;
+Index count = m.cwiseNotEqual(MatrixXi::Identity(2,2)).count();
+cout << "Number of coefficients that are not equal: " << count << endl;