title: Find longest common prefix?
body: <p>In two strings:</p>
  
  <blockquote>
    <p>"Mary Had a Little Lamb" <br />"Mary Had a Big Lamb"</p>
  </blockquote>
  
  <p>should return</p>
  
  <blockquote>
    <p>"Mary Had a "</p>
  </blockquote>