message: pickle function for LeftOfLabelFunction
diff: @@ -194,7 +194,16 @@ void python_ltl(py::module m) {
  py::class_<LeftOfLabelFunction, BaseLabelFunction,
  std::shared_ptr<LeftOfLabelFunction>>(m, "LeftOfLabelFunction")
  - .def(py::init<const std::string&>());
  + .def(py::init<const std::string&>())
  + .def(py::pickle(
  + [](const LeftOfLabelFunction& b) {
  + return py::make_tuple(b.GetLabelStr());
  + },
  + [](py::tuple t) {
  + if (t.size() != 1)
  + throw std::runtime_error("Invalid label evaluator state!");
  + return new LeftOfLabelFunction(t[0].cast<std::string>());
  + }));
  py::class_<BehindOfLabelFunction, BaseLabelFunction,
  std::shared_ptr<BehindOfLabelFunction>>(m, "BehindOfLabelFunction")
  