ADD: new track message, Entity class and Position class

libs/geographiclib/examples/example-Utility.cpp

@@ -0,0 +1,21 @@
+// Example of using the GeographicLib::Utility class
+
+#include <iostream>
+#include <exception>
+#include <GeographicLib/Utility.hpp>
+
+using namespace std;
+using namespace GeographicLib;
+
+int main() {
+  try {
+    int
+      d1 = Utility::day(1939, 9, 3),  // Britain declares war on Germany
+      d2 = Utility::day(1945, 8, 15); // Japan surrenders
+    cout << d2 - d1 << "\n";          // Length of Second World War for Britain
+  }
+  catch (const exception& e) {
+    cerr << "Caught exception: " << e.what() << "\n";
+    return 1;
+  }
+}