change to MIT license

change to MIT license

Add a proper license instead of the just saying 'public domain'
(arguably unfulfilling, see http://www.linuxjournal.com/article/6225).
The MIT or X11 license is similar in intent to the perceived PD,
and should provide all if not more rights to users.
It's essentially the same as the 2-clause BSD and ISC licenses.

With consent of the original copyright holder Juerd Waalboer:
> BTW, mocht je een echte licentie willen gebruiken, dan stel ik MIT
> voor als je je daar zelf in kunt vinden