title: Finding day of the week for a datetime64
body: <p>Apologies if this is an easy one but I can't see anything in the <code>numpy</code> documentation. I have a <code>datetime64</code> and I'd like to find out which day of the week it is. </p>
  
  <p>Unlike python <code>datetime</code>, <code>datetime64</code> doesn't seem to have a <code>.weekday()</code> function. However it does have a <code>busday_offset()</code> function, which implies it must know behind-the-scenes what day of the week a given date is. Any help greatly appreciated.</p>