Add League URL.

README.md

 
 * [Purl](https://github.com/jwage/purl) - A URL manipulation library.
 * [PHP Domain Parser](https://github.com/jeremykendall/php-domain-parser) - A domain suffix parser library.
+* [Url](https://github.com/thephpleague/url) - A simple URL manipulation library.
 
 ## Email
 *Libraries for sending and parsing email.*