title: get key value pairs from xml using linq
body: <p>How can i extract key value pairs from this xml example using linq:</p>
  
  <pre><code>&lt;foo&gt;
  &lt;add key="key1" Value="val1"/&gt;
  &lt;add key="key2" Value="val2"/&gt;
  &lt;add key="key3" Value="val3"/&gt;
  &lt;foo/&gt;
  </code></pre>