title: How to handle keyboard events in OpenLayers 3?
body: <p>I would like to activate/deactivate an <code>ol.interaction</code> based on the fact a key is pressed/released on the map.
  I already did something like </p>
  
  <pre><code>document.addEventListener('keydown',... myIneteraction.setActive(true) ...)
  </code></pre>
  
  <p>...but was wondering if there is a cleaner approach (eg. listening on some native <code>ol.[...]</code> event). I don't understand when (if ever, apparently never) keyboard events are fired by the <code>ol.Map</code>.</p>