Add support for adding messages in closure rules

This PR makes it possible to add messages in a closure.

~~~php
        $filter->setRule(
            'foo',
            'Enter Foo correctly',
            function ($value) use ($filter) {
                $pass = true;
                if ($value == '') {
                    $filter->addMessages('foo', 'Foo is required');
                    $pass = false;
                }
                
                if (! ctype_alpha($value)) {
                    $filter->addMessages('foo', 'Foo should be alpha only');
                    $pass = false;
                }
                return $pass;
            }
        );
~~~