title: Sorting list by alphabetical order, with special case for certain starting letter
body: <p>Given a list of strings, I want to return a list with the strings in sorted order, except group all the strings that begin with 'x' first. </p>
  
  <p>For example:</p>
  
  <pre><code>['mix', 'xyz', 'apple', 'xanadu', 'aardvark']
  </code></pre>
  
  <p>Should yield:</p>
  
  <pre><code>['xanadu', 'xyz', 'aardvark', 'apple', 'mix']
  </code></pre>
  
  <p>I know it can be done by making 2 lists and sorting each of them before combining them, but I'm not sure how to write the condition in which 'x' is the first character. </p>