Allow the JSON encoder/decoder to be easily changed

src/motion/marshal.py

@@ -13,18 +13,21 @@ def __init__(self, error, payload):
 
 class JSONMarshal(object):
     """Simple JSON Marshal"""
+    JSONEncoder = None
+    JSONDecoder = None
+
     def to_bytes(self, event_name, payload):
         try:
             return json.dumps({
                 'event_name': event_name,
                 'payload': payload
-            })
+            }, cls=self.JSONEncoder)
         except ValueError:
             raise MarshalFailure("Could not convert payload to JSON", payload)
 
     def to_native(self, payload):
         try:
-            native = json.loads(payload)
+            native = json.loads(payload, cls=self.JSONDecoder)
         except ValueError:
             raise MarshalFailure("Could not load valid JSON from payload", payload)
         return native['event_name'], native['payload']