title: Split pandas column by separator for different string sizes
body: <p>How can one split a column like <code>df.value</code> </p>
  
  <pre><code>value
  --------
  Top/Animals/Cat
  Top/Dog
  Pig/Guineea/Piglet
  </code></pre>
  
  <p>into multiple columns </p>
  
  <pre><code>val1 |   val2   | val3 |
  Top    Animals     Cat
  NaN      Top       Dog
  Pig    Guineea    Piglet
  </code></pre>
  
  <p>such that I have the number of columns of the longest string and NaN where other strings are not the same length? </p>