title: split dataframe when number is lower than the previous number
body: <p>I have a series like this:
  <code>test = pd.Series([2.4,5.6,8.8,25.6,53.6,1.7,5.7,8.9])</code></p>
  
  <p>I want to split it into two series at the point where the next number is smaller than the previous one. This only happens once in any series, but it does not happen at a reliable location (could be the 7th place, 4th, etc).</p>
  
  <p>The result should look like this:</p>
  
  <pre><code>test1
  2.4
  5.6
  8.8
  25.6
  53.6
  </code></pre>
  
  <p>and</p>
  
  <pre><code>test2
  1.7
  5.7
  8.9
  </code></pre>