title: Pandas Datetime Interval Resample to Seconds
body: <p>Given the following dataframe:</p>
  
  <pre><code>import pandas as pd
  
  pd.DataFrame({"start": ["2017-01-01 13:09:01", "2017-01-01 13:09:07", "2017-01-01 13:09:12"],
           "end":    ["2017-01-01 13:09:05", "2017-01-01 13:09:09", "2017-01-01 13:09:14"],
           "status": ["OK", "ERROR", "OK"]})
  </code></pre>
  
  <p>HAVE:</p>
  
  <pre><code>| start               | end                 | status |
  |---------------------|---------------------|--------|
  | 2017-01-01 13:09:01 | 2017-01-01 13:09:05 | OK     |
  | 2017-01-01 13:09:07 | 2017-01-01 13:09:09 | ERROR  | 
  | 2017-01-01 13:09:12 | 2017-01-01 13:09:14 | OK     |
  </code></pre>
  
  <p>I want to convert it to another format, that is, "unfold" the intervals and make them into a DatetimeIndex, and resample the data. The result should look like this:</p>
  
  <p>WANT: </p>
  
  <pre><code>|                     | status    |
  |---------------------|-----------|
  | 2017-01-01 13:09:01 | OK        |
  | 2017-01-01 13:09:02 | OK        |
  | 2017-01-01 13:09:03 | OK        |
  | 2017-01-01 13:09:04 | OK        |
  | 2017-01-01 13:09:05 | OK        |
  | 2017-01-01 13:09:06 | NAN       |
  | 2017-01-01 13:09:07 | ERROR     |
  | 2017-01-01 13:09:08 | ERROR     |
  | 2017-01-01 13:09:09 | ERROR     |
  | 2017-01-01 13:09:10 | NAN       |
  | 2017-01-01 13:09:11 | NAN       |
  | 2017-01-01 13:09:12 | OK        |
  | 2017-01-01 13:09:13 | OK        |
  | 2017-01-01 13:09:14 | OK        |
  </code></pre>
  
  <p>Any help is very much appreciated! </p>