Mark notifications as read.

        CURRENT UNSUPPORTED:
        https://github.com/kippt/api-documentation/blob/master/endpoints/notifications/POST_notifications.md

def mark_read(self):
        """ Mark notifications as read.

        CURRENT UNSUPPORTED:
        https://github.com/kippt/api-documentation/blob/master/endpoints/notifications/POST_notifications.md

        """
        # Obviously remove the exception when Kippt says the support it.
        raise NotImplementedError(
            "The Kippt API does not yet support marking notifications as read."
        )

        data = json.dumps({"action": "mark_seen"})
        r = requests.post(
            "https://kippt.com/api/notifications",
            headers=self.kippt.header,
            data=data
        )
        return (r.json())