Recovered a minimal support for Doxygen.

Removed MSGPACK_API_VERSION_NAMESPACE(v1) from doxygen build.
It seems that Doxygen cannot parse a complicated macro such as MSGPACK_API_VERSION_NAMESPACE.

Added EXTRACT_ALL=YES to Doxyfle.
Added INPUT configuration variable that is point to include directory to Doxyfile.

include/msgpack/adaptor/cpp11/unordered_map.hpp

@@ -26,7 +26,9 @@
 
 namespace msgpack {
 
+/// @cond
 MSGPACK_API_VERSION_NAMESPACE(v1) {
+/// @endcond
 
 template <typename K, typename V>
 inline msgpack::object const& operator>> (msgpack::object const& o, std::unordered_map<K, V>& v)
@@ -134,7 +136,9 @@ inline void operator<< (msgpack::object::with_zone& o, const std::unordered_mult
     }
 }
 
+/// @cond
 }  // MSGPACK_API_VERSION_NAMESPACE(v1)
+/// @endcond
 
 }  // namespace msgpack