title: howler.js for multiple audio files
body: <p>It works for for a single file: </p>
  
  <pre><code>&lt;button id="btn"&gt;Play&lt;/button&gt;
  &lt;script&gt;
   var btn = new Howl({urls: ['http://www.javascriptoo.com/application/html/btn.wav']})
  document.getElementById('btn').onclick=function(){btn.play()}
  &lt;/script&gt;
  </code></pre>
  
  <p>But I need to play multiple files:</p>
  
  <pre><code>&lt;button id="btn2"&gt;Play&lt;/button&gt;
  &lt;button id="btn3"&gt;Play&lt;/button&gt;
  &lt;button id="btn23"&gt;Play&lt;/button&gt;
  </code></pre>
  
  <p><strong>Is it any easy way to solve it?</strong></p>