Add tests for url generated with named route.
Allow specifying route name when using url array.
Refactor code to allow passing url fragmenent for named routes.
Update docblock.
Remove redudant usage forms for Router::url().

You can no longer specify route name as string for first argument.
Minor optimization.
Use Request::env() instead of overriding globals.
Merge pull request #4220 from cakephp/3.0-router-url

3.0 router url