Bind target now supports simple callback on change - which I'm using to trigger events

I'm combining bind.js with min.js and on value change I'm triggering a global event:

```js
$.on('foo', function () {
  // do the foo
});

// ... elsewhere

new Bind({
  me: {
    score: 0,
    name: 'rem'
  }
}, {
  'me.score': function (score) {
    $.trigger('foo', score);
    console.log('-> updated value me.score: ' + score);
  }
}
```