Re-designed user types dispatching mechanism.

msgpakc-c 0.5.9 or older uses ADL.
msgpack-c 1.0.x uses overloading with header files ordering.
msgpack-c 1.1.x uses functor with class template specialization.

test/object_with_zone.cpp

@@ -1,4 +1,4 @@
-#include <msgpack_fwd.hpp>
+#include <msgpack.hpp>
 #include <gtest/gtest.h>
 #include <cmath>
 
@@ -40,9 +40,6 @@ MSGPACK_ADD_ENUM(outer_enum_class::enum_class_test);
 
 
 
-#include <msgpack.hpp>
-
-
 using namespace std;
 
 const unsigned int kLoop = 1000;