Initializes a Flask object `app`: binds the HTML prettifying with
        app.after_request.

        :param app: The Flask application object.

def init_app(self, app):
        """
        Initializes a Flask object `app`: binds the HTML prettifying with
        app.after_request.

        :param app: The Flask application object.
        """
        app.config.setdefault('PRETTIFY', False)

        if app.config['PRETTIFY']:
            app.after_request(self._prettify_response)