pypi: Release version 0.5.4.

Starting now, we now also have a CHANGELOG to record major changes
to the zulip package.

zulip/zulip/__init__.py

@@ -42,7 +42,7 @@ import logging
 import six
 from typing import Any, Callable, Dict, Iterable, IO, List, Mapping, Optional, Text, Tuple, Union
 
-__version__ = "0.5.3"
+__version__ = "0.5.4"
 
 logger = logging.getLogger(__name__)