title: filtering a pandas Dataframe based on date value
body: <p>I have the following data imported from a csv file using pandas <code>read_csv</code>:</p>
  
  <pre><code> instrument         type   from_date  to_date   
  0   96000001    W/D &amp; V/L  19951227  19960102
  1   96000002   DEED TRUST  19951227  19960102
  2   96000003  WARNTY DEED  19951228  19960102
  3   96000004   DEED TRUST  19951228  19960102
  4   96000005    W/D &amp; V/L  19951228  19960102
  </code></pre>
  
  <p>I would like to select those rows that fit a date or date range. For instance I want to 
  select only those rows with the date <code>19951227</code> in the <code>from_date</code> column or select days that range from <code>from_date</code> of <code>19951227</code> to <code>to_date</code> <code>19960102</code>.</p>
  
  <p>How would I do this?</p>