Added the ability to define callbacks inline on filters for Controllers.

With this pull request you will now be able to do the following:

````
$this->filter('before', function()
{
    return Redirect::to('http://google.com');
});

$this->filter('before', function($foo)
{
    return Redirect::to($foo);
}, array('http://google.com'));
````

This is extremely useful when you have a one-off filter than needs to be used on a controller, thus placing in the routes.php file makes no sense.