message: Simplify bindings of LandmarkMapper c'tor
  It's now using string and not fs::path anymore.
diff: @@ -63,9 +63,7 @@ PYBIND11_PLUGIN(eos) {
  py::module core_module = eos_module.def_submodule("core", "Essential functions and classes to work with 3D face models and landmarks.");
  py::class_<core::LandmarkMapper>(core_module, "LandmarkMapper", "Represents a mapping from one kind of landmarks to a different format(e.g.model vertices).")
  .def(py::init<>(), "Constructs a new landmark mapper that performs an identity mapping, that is, its output is the same as the input.")
  - .def("__init__", [](core::LandmarkMapper& instance, std::string filename) { // wrap the fs::path c'tor with std::string
  - new (&instance) core::LandmarkMapper(filename);
  - }, "Constructs a new landmark mapper from a file containing mappings from one set of landmark identifiers to another.", py::arg("filename"))
  + .def(py::init<std::string>(), "Constructs a new landmark mapper from a file containing mappings from one set of landmark identifiers to another.", py::arg("filename"))
  // We can't expose the convert member function yet - need std::optional (or some trick with self/this and a lambda)
  ;
  