title: Conditional DateFormatter in Bokeh tables
body: <p>I can do a static choice for my date formatter in Bokeh tables</p>
  <pre><code>TableColumn(field=xdata, title=xdata, formatter=DateFormatter(format=&quot;%a, %e %b %y&quot;)),
  </code></pre>
  <p>but I would like to do something more dynamic, showing the time of the day if it is less than few hours away from the current time, else showing the full date (day+time)</p>
  <p>Other questions seem to focus on cell background and stuff like that depending on conditions, so I cannot find a previously asked question that really fits for this.</p>