Added `yii\web\View::clear()`
Update url.md

Documentation updates
Use a hidden link to support grid filtering.
Fixes #706: Added `yii\widgets\Pjax` and enhanced `GridView` to work with `Pjax` to support AJAX-update
Merge branch 'master' of git://github.com/yiisoft/yii2
Merge pull request #2203 from arisk/patch-4

Update url.md
minor fixes.