title: Iterating over all the keys of a map
body: <p>Is there a way to get a list of all the keys in a Go language map?  The number of elements is given by <code>len()</code>, but if I have a map like:</p>
  
  <pre><code>m := map[string]string{ "key1":"val1", "key2":"val2" };
  </code></pre>
  
  <p>How do I iterate over all the keys?</p>