title: Is there an easy way to make nested array flat?
body: <p>That is to make this:</p>
  
  <p><code>[ ['dog','cat', ['chicken', 'bear'] ],['mouse','horse'] ]</code></p>
  
  <p>into: </p>
  
  <p><code>['dog','cat','chicken','bear','mouse','horse']</code></p>