[READY] \yii\behaviors\SluggableBehavior

Usage:

```php
class Post extends ActiveRecord
{
    public function behaviors() {
        return [
            [
                'class' => Sluggable::className(),
                // use this
                'attribute' => 'title',
                // or this to customize
                // 'value' => function ($event) {
                //     return Inflector::slug($this->title);
                // },
            ],
        ];
    }
}
```
> Slug does not need validation 

SURE? Check this coding reception:

```php
    public function rules()
    {
        return [
            ['slug', 'required'],
            ['slug', 'unique'],

            ['title', 'trim'],
            ['title', 'required'],
            ['title', 'string', 'max' => 255],
            ['title', function () {
                if ($this->hasErrors('slug')) {
                    $this->addError('title', Yii::t('app', 'Title is invalid.'));
                }
            }],
        ];
    }
```

Now try to get this functional in later events.