Python: bytearray body support for ASGI module.

@filiphanes requested support for bytearray
and memoryview in the request body here:
<https://github.com/nginx/unit/issues/648>

This patch implements bytearray body support only.
Memoryview body still need to be implemented.

docs/changes.xml

@@ -78,6 +78,12 @@ can be used as a unique request identifier.
 </para>
 </change>
 
+<change type="feature">
+<para>
+bytearray in response body for ASGI applications.
+</para>
+</change>
+
 <change type="feature">
 <para>
 ServerRequest.flushHeaders() implemented in Node.js module to make it compatible