Inject a message

        :params string msg_content: The entire message's content.
        :params string folder: Folder pathname (starts with '/') or folder ID

def add_message(self, msg_content, folder, **kwargs):
        """ Inject a message

        :params string msg_content: The entire message's content.
        :params string folder: Folder pathname (starts with '/') or folder ID
        """
        content = {'m': kwargs}
        content['m']['l'] = str(folder)
        content['m']['content'] = {'_content': msg_content}

        return self.request('AddMsg', content)