title: Map both keys and values of a Scala Map
body: <p>Scala's <code>MapLike</code> trait has a method</p>
  
  <pre><code>mapValues [C] (f: (B) ⇒ C): Map[A, C] 
  </code></pre>
  
  <p>But I sometimes want a different type:</p>
  
  <pre><code>mapKeysAndValues [C] (f: (A, B) ⇒ C): Map[A, C] 
  </code></pre>
  
  <p>Is there a simple way to do this which I am missing? Of course, this can be done with a fold.</p>