title: Convert std::string to QString
body: <p>I've got an <code>std::string content</code> that I know contains UTF-8 data. I want to convert it to a <a href="http://doc.qt.io/qt-4.8/qstring.html" rel="noreferrer"><code>QString</code></a>. How do I do that, avoiding the from-ASCII conversion in Qt?</p>