Add LogzioException class

Currently the module raises generic Exception (very "don't do it")

logzio/exceptions.py

@@ -0,0 +1,2 @@
+class LogzioException(Exception):
+    pass

logzio/handler.py

@@ -6,6 +6,7 @@ import traceback
 import logging.handlers
 
 from .sender import LogzioSender
+from .exceptions import LogzioException
 
 
 class LogzioHandler(logging.Handler):