Fixed #204, #202.

enum support had been incomplete.
This fix made enum support complete.

Replaced int with auto on c++11 scoped enum.
Replaced template specializations with function overloads on operator<< and operator>> for enum.

enum can convert to object with and without zone.

When you want to adapt enum, you need to write as follows:

// NOT msgpack.hpp

enum yourenum {
    elem
};

MSGPACK_ADD_ENUM(yourenum);

// msgpack.hpp should be included after MSGPACK_ADD_ENUM(...)

int main() {
    msgpack::object obj(yourenum::elem);
}

erb/cpp03_define.hpp.erb

@@ -20,6 +20,7 @@
 
 #include "msgpack/versioning.hpp"
 #include "msgpack/adaptor/msgpack_tuple_fwd.hpp"
+#include "msgpack/adaptor/int_fwd.hpp"
 #include "msgpack/object_fwd.hpp"
 
 #define MSGPACK_DEFINE(...) \
@@ -42,7 +43,6 @@
 #define MSGPACK_ADD_ENUM(enum) \
   namespace msgpack { \
   MSGPACK_API_VERSION_NAMESPACE(v1) { \
-    template <> \
     inline object const& operator>> (object const& o, enum& v) \
     { \
       int tmp; \
@@ -50,7 +50,10 @@
       v = static_cast<enum>(tmp); \
       return o; \
     } \
-    template <> \
+    inline void operator<< (object& o, const enum& v) \
+    { \
+      o << static_cast<int>(v); \
+    } \
     inline void operator<< (object::with_zone& o, const enum& v) \
     { \
       o << static_cast<int>(v); \