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.cpp

@@ -1,4 +1,4 @@
-#include <msgpack_fwd.hpp>
+#include <msgpack.hpp>
 #include <gtest/gtest.h>
 
 
@@ -34,10 +34,6 @@ MSGPACK_ADD_ENUM(outer_enum_class::enum_class_test);
 
 #endif // !defined(MSGPACK_USE_CPP03)
 
-
-
-#include <msgpack.hpp>
-
 struct myclass {
     myclass() : num(0), str("default") { }