title: Add CREATED date property to TODOs in org-mode
body: <p>I read the org-mode manual but couldn't find an easy way to add a CREATED field to newly created TODOs. In combination with <code>org-log-done</code> one could then compute the time it took to close a particular TODO. This is especially useful when using archive files. </p>
  
  <p>Example:</p>
  
  <pre><code>* TODO Do something
    CREATED:  [2012-09-02 Sun 23:02]
  * DONE Do something else
    CREATED: [2012-09-02 Sun 20:02]
    CLOSED: [2012-09-02 Sun 22:02]
  </code></pre>
  
  <p>I would expect the CREATED field to be added to new tasks (tasks which don't have that field) whenever the file is saved.</p>
  
  <p>Any suggestions on how to achieve this? Using something like Git is not a solution for me to track the creations of TODOS.</p>