+ licence to headers

> [The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.](https://github.com/jonschlinkert/remarkable/blob/master/LICENSE)

But I think `license MIT` is fine; devs & CS lawyers know what this means.
The `!` & `@license` are flags for minifiers & concocters to keep the legal notification.
Sorry to lengthen your header; very admirable of you to keep it small!