Dev/guess clusters (#355)

- exposing ClusterVector::empty in python
- added member guess_n_clusters

python/src/bind_ClusterVector.hpp

@@ -72,6 +72,7 @@ void define_ClusterVector(py::module &m, const std::string &typestr) {
             R"(calculates sum of 2x2 subcluster with highest energy and index relative to cluster center 0: top_left, 1: top_right, 2: bottom_left, 3: bottom_right
             )")
         .def_property_readonly("size", &ClusterVector<ClusterType>::size)
+        .def("empty", &ClusterVector<ClusterType>::empty)
         .def("item_size", &ClusterVector<ClusterType>::item_size)
         .def_property_readonly("fmt",
                                [typestr](ClusterVector<ClusterType> &self) {
@@ -169,4 +170,4 @@ void define_3x3_reduction(py::module &m) {
         py::arg("clustervector"));
 }
 
-#pragma GCC diagnostic pop
+#pragma GCC diagnostic pop