title: Function to split text in cell and create column
body: <p>I have a Google Spreadsheet with rows like this:</p>
  
  <pre><code>| sth1, sth2 |
  | sth4       |
  | sth1, sth3 |
  | sth4       |
  </code></pre>
  
  <p>And I want to split each cell in this column and create new column like this:</p>
  
  <pre><code>| sth1 |
  | sth2 |
  | sth4 |
  | sth1 |
  | sth3 |
  | sth4 |
  </code></pre>
  
  <p>Can someone show me how to do this?</p>