Add seemingly functional but hacky gc

src/evaluate.c

@@ -35,6 +35,7 @@ struct ucl_object *ucl_evaluate_builtin_form(struct ucl_state *state, struct ucl
             i++;
         }
         result = ucl_progn(fun_state, fun_forms);
+        ucl_state_delete(fun_state);
     } else {
         assert(0);
     }