Add compatibility with regular (non structured) logging usage

Part of #8.

Author: EvaSDK

fluent/handler.py

@@ -51,7 +51,7 @@ def _structuring(self, data, msg):
             try:
                 self._add_dic(data, json.loads(str(msg)))
             except (ValueError, json.JSONDecodeError):
-                pass
+                self._add_dic(data, {'message': msg})
 
     @staticmethod
     def _add_dic(data, dic):