Fix broken links with external urls (#75)
Fix broken links with external urls (#75)

When an url in the guide is refering to an url out of the guide project itself, avoid parsing url to keep it working (used in side nav bar).

Example:
[Advanced Project Template](https://github.com/yiisoft/yii2-app-advanced/blob/master/docs/guide/README.md)
yiisoft/yii2-apidoc