Add option to get a valid json dump.

Alternative approach to #1

pylevel2/api.py

@@ -11,9 +11,9 @@ import json
 class DatetimeEncoder(json.JSONEncoder):
     def default(self, obj):
         if isinstance(obj, datetime):
-            return obj.isoformat(' ')
+            return obj.strftime('%Y-%m-%d %H:%M:%S')
         elif isinstance(obj, date):
-            return obj.isoformat()
+            return obj.strftime('%Y-%m-%d')
         # Let the base class default method raise the TypeError
         return json.JSONEncoder.default(self, obj)