add method current

examples 

current url post/list?sort=date
```php
Url::current(['find'=>'toys']);         // /post/list?sort=date&find=toys
Url::current(['find=toys&price=2']);    // /post/list?sort=date&find=toys&price=2  
Url::current(['find=toys&price=2'],'sort'); // /post/list?find=toys&price=2
```