Use stringByAddingPercentEscapesUsingEncoding when creating NSURL from NSString 

Consider an url like this, appearing in my JSON source: http://www.visir.is/jordan-slaer-milljard-af-villunni-sinni-|-myndir/article/2013130709873

This won't result in a valid NSURL. Doing stringByAddingPercentEscapesUsingEncoding seems like a smart thing to do in all cases.