Make qdoc output \keyword anchors at the tops of the comments

Currently, qdoc processes \keyword and \target the same way. The negative effect of this is that when either command appears at the top of a qdoc comment, the anchor it generates in the html file is just above the details section on the html page. This is usually wrong, especially for \keyword commands, where the anchor generated should always be at the top of the page/text where the \keyword appears. This update implements that. \target anchors are meant to be used when the anchor should appear somewhere in the middle of the page/text, exactly where the \target command appears.