added 'masonry.resize'

problem: binding masoned container width with other elements

```js
// first 'masonry.resize' event can not be catched.
$('#container ul').masonry({
  itemSelector: '.item',
  isFitWidth: true,
}).on('masonry.resize', function (e, width) {
  $('#header').css('width', width)
})
```

so I added an onResize option

```js
$('#container ul').masonry({
  itemSelector: '.item',
  isFitWidth: true,
  onResize: function (e, width) {
    $('#header').css('width', width)
  }
})
```