title: Iterate Go map get index
body: <p>In order to use <code>revel</code>'s <a href="https://revel.github.io/manual/templates.html#even" rel="noreferrer"><code>even</code></a> keyword in templates I would like to get the index of a map entry when iterating with <code>range</code>. Is there any way to do so? 
  My map has the structure:</p>
  
  <pre><code>map[string][]string
  </code></pre>