added mootools.fittext.js

A complete port of FitText.js to mootools.  Unlike [Pull request 4](https://github.com/davatron5000/FitText.js/pull/4), this maintains the API, so people can use FitText exactly the same, whether they are using jQuery or Mootools.  This still required a separate file, though if we work too much on abstraction from the frameworks, we might as well write a framework-agnostic plugin (which isn't a bad idea, actually)... But this is close enough at least :)