Fix logging

- Following advice here: https://docs.python.org/3/howto/logging.html#configuring-logging-for-a-library
- Renamed the logger: client -> fbchat
- Remove logging_level init parameter from Client
- Use print instead of log.info in examples

fbchat/_graphql.py

@@ -1,5 +1,6 @@
 import json
 import re
+from ._core import log
 from . import _util
 from ._exception import FBchatException
 
@@ -54,7 +55,7 @@ def response_to_json(content):
         else:
             rtn[int(key[1:])] = value["data"]
 
-    _util.log.debug(rtn)
+    log.debug(rtn)
 
     return rtn