Fix the prototype filefive to return the modified instance

I made the change on `$.fn.filefive` so the plugin allows using:

````javascript
    $(selector).filefive().files()
````

Before, by returning `this.each()` on the prototype method `files()` was added to the new instance created on `$.filefive` and never returned.

As a test you can now use `$(this).filefive();` on the [example page](https://github.com/NicoSantangelo/jquery-filefive/blob/master/examples.html#L42)