Add \Illuminate\Support\Collection::getDot like array_get()

Add \Illuminate\Support\Collection::getDot() like array_get(). So pity, we havnt method to get value of nested array in Collection.
Not always going to work (this as well). E.g: eloquent result collection. Personally I would just do

```php
$fullname = data_get($users, '0.fullname'); // etc
```