Work on extern support for userdata functions

src/UserData/UserDataFunction.cpp

@@ -1,2 +1,12 @@
 
 #include "UserDataFunction.hpp"
+
+using namespace Porygon::Evaluation;
+
+namespace Porygon::UserData{
+    extern "C" {
+        EvalValue * CreateFunctionEvalValue(Evaluation::EvalValue* (*func)(void* , EvalValue* [], int ), void* obj) {
+            return new UserDataFunction(func, obj);
+        }
+    }
+}