updated public symbols

Author: miguelgrinberg

socketio/__init__.py

@@ -10,6 +10,7 @@
 from .namespace import Namespace
 if sys.version_info >= (3, 5):  # pragma: no cover
     from .asyncio_server import AsyncServer
+    from .asyncio_namespace import AsyncNamespace
 else:  # pragma: no cover
     AsyncServer = None
 
@@ -20,3 +21,4 @@
            'Namespace']
 if AsyncServer is not None:  # pragma: no cover
     __all__.append('AsyncServer')
+    __all__.append('AsyncNamespace')