title: Calculate time range in org-mode table
body: <p>Given a table that has a column of time ranges e.g.:</p>
  
  <pre><code>|  &lt;2015-10-02&gt;--&lt;2015-10-24&gt; |
  |  &lt;2015-10-05&gt;--&lt;2015-10-20&gt; |
  ....
  </code></pre>
  
  <p>how can I create a column showing the results of org-evalute-time-range?</p>
  
  <p>If I attempt something like:
      #+TBLFM: $2='(org-evaluate-time-range $1)</p>
  
  <p>the 2nd column is populated with </p>
  
  <pre><code> Time difference inserted
  </code></pre>
  
  <p>in every row.</p>
  
  <p>It would also be nice to generate the same result from two different columns with, say, <code>start date</code> and <code>end date</code> instead of creating one column of time ranges out of those two. </p>