fix the removal of keyword::one_string in the python bindings

source/_bindings.cc

@@ -90,7 +90,6 @@ PYBIND11_MODULE(_lephare, mod) {
     .def("split_long", &keyword::split_long)
     .def("split_double", &keyword::split_double)
     .def("split_bool", &keyword::split_bool)
-    .def("one_string", &keyword::one_string)
     .def("__repr__",
 	 [](const keyword &a) {
 	   return "("+a.name+", "+ a.value +")";