Create a new comment, associating it with a specific message.

def create_comment(self, post_id, body):
        """
        Create a new comment, associating it with a specific message.
        """
        path = '/msg/create_comment'
        req = ET.Element('request')
        comment = ET.SubElement(req, 'comment')
        ET.SubElement(comment, 'post-id').text = str(int(post_id))
        ET.SubElement(comment, 'body').text = str(body)
        return self._request(path, req)