title: Convert interval datetime values to any-frequency time series
body: <p>I have the following data structure: </p>
  
  <pre><code>2011-01-01 00:00, 2011-01-20 00:00, 200   # days-range
  2011-01-20 00:00, 2011-03-08 00:00, 1288  # days-range
  2011-04-11 00:00, 2012-01-08 00:00, 5987  # days-range
  
  2012-02-01 00:00, 2012-02-01 01:00, 7     # hourly-range
  2012-02-01 02:00, 2012-02-01 02:30, 3     # hourly-range
  </code></pre>
  
  <p>This is interval with <strong>start date</strong>, <strong>end date</strong> and <strong>value</strong> (some metric recorded between dates).</p>
  
  <p>For further data analysis I need to generate time series with required frequency:
  <strong>monthly/daily/hourly/half-hourly</strong> time series. For example, hourly data: </p>
  
  <pre><code>2011-01-01 00:00, 2 
  2011-01-01 01:00, 6
  2011-01-01 02:00, 5
  ...
  </code></pre>
  
  <p><strong>Is there any python lib which can help to implement this kind of data transformation?</strong></p>