ADD: new track message, Entity class and Position class

libs/geographiclib/man/dummy.usage.in

@@ -0,0 +1,8 @@
+// Dummy usage file to be used when the man page isn't available
+
+int usage(int retval, bool /* brief */) {
+  ( retval ? std::cerr : std::cout )
+    << "For full documentation on @TOOL@, see\n"
+    << "    https://geographiclib.sourceforge.io/C++/@PROJECT_VERSION@/@TOOL@.1.html\n";
+  return retval;
+}