title: Slice pandas dataframe in groups of consecutive values
body: <p>I have a dataframe containing sections of consecutive values that eventually "skip" (that is, are increased by more than 1). I would like to split the dataframe, similar to <code>groupby</code> function (alphabetic indexing just for show):</p>
  
  <pre><code>    A
  a   1
  b   2
  c   3
  d   6
  e   7
  f   8
  g   11
  h   12
  i   13
  
  # would return
  
  a   1
  b   2
  c   3
  -----
  d   6
  e   7
  f   8
  -----
  g   11
  h   12
  i   13
  </code></pre>