added json encoder for PoyCubes

python/polycube_encoder.py

@@ -0,0 +1,9 @@
+from json import JSONEncoder
+from typing import Any
+from polycube import PolyCube
+
+class PolyCubeEncdoder(JSONEncoder):
+    def default(self, o: Any) -> Any:
+        if isinstance(o, PolyCube):
+            return list(o.cubes)
+        return super().default(o)