Relative urls don't work

This works fine:
```
[url=https://localhost/www]text[/url]
[img]https://localhost/www/img[/img]
[url=https://localhost/www][img]https://localhost/www/img[/img][/url]
```

This does not:
```
[url=/www]text[/url]
[img]/www/img[/img]
[url=/www][img]/www/img[/img][/url]
```

Please fix or hint so I can fix it for us all faster