Add implementation for respond_to_missing?

src/kernel.c

@@ -965,7 +965,7 @@ obj_respond_to(mrb_state *mrb, mrb_value self)
   mrb_value *argv;
   int argc;
   mrb_value mid, priv;
-  mrb_sym id;
+  mrb_sym id, rtm_id;
   mrb_bool respond_to_p;
 
   mrb_get_args(mrb, "*", &argv, &argc);
@@ -976,6 +976,13 @@ obj_respond_to(mrb_state *mrb, mrb_value self)
 
   respond_to_p = basic_obj_respond_to(mrb, self, id, !mrb_test(priv));
 
+  if(!respond_to_p) {
+    rtm_id = mrb_intern2(mrb, "respond_to_missing?", 19);
+    if(basic_obj_respond_to(mrb, self, rtm_id, !mrb_test(priv))) {
+      return mrb_funcall_argv(mrb, self, rtm_id, argc, argv);
+    }
+  }
+
   return mrb_bool_value(respond_to_p);
 }