ADD: new track message, Entity class and Position class

libs/geographiclib/examples/example-Geodesic-small.cpp

@@ -0,0 +1,18 @@
+// Small example of using the GeographicLib::Geodesic class
+
+#include <iostream>
+#include <GeographicLib/Geodesic.hpp>
+
+using namespace std;
+using namespace GeographicLib;
+
+int main() {
+  const Geodesic& geod = Geodesic::WGS84();
+  // Distance from JFK to LHR
+  double
+    lat1 = 40.6, lon1 = -73.8, // JFK Airport
+    lat2 = 51.6, lon2 = -0.5;  // LHR Airport
+  double s12;
+  geod.Inverse(lat1, lon1, lat2, lon2, s12);
+  cout << s12 / 1000 << " km\n";
+}