title: chrono C++11 version of matlabs datenum
body: <p>Is there a <code>C++11</code> version of matlabs <code>datenum</code> function in <code>#include&lt;chrono&gt;</code>? </p>
  
  <p>I already know it exists in boost thanks to this <a href="https://stackoverflow.com/questions/13242583/calculating-the-date-from-day-number">post</a></p>