title: Dat.gui add slider for each element in array
body: <p>So I have a javascript object that looks like this</p>
  
  <pre><code>var parameters = {bgColor: 0x5886a0, 
    ambientColor:0xffffff,
    opacityCS:[ 1.0, 1.0, 1.0, 1.0, 1.0, 1.0], 
    whiteThreshold:[160,160,160,160,160,160] };
  </code></pre>
  
  <p>I would like to add a slider for each opacityCs and for each whiteThreshold.</p>
  
  <p>For other parameters is easy </p>
  
  <pre><code>gui.addColor( parameters, 'ambientColor' ).onChange( function(){/**/});
  </code></pre>
  
  <p>or</p>
  
  <pre><code>gui.add( parameters, 'variable', -0.5, 0.5, 0.005  );
  </code></pre>
  
  <p>But I dont find the way to add elements of arrays. Can anyone help?</p>