title: Convert upper case words to title case
body: <p>I want to change this:</p>
  
  <pre><code>input &lt;- c("Théodore Agrippa d'AUBIGNÉ", "Vital d'AUDIGUIER DE LA MENOR")
  </code></pre>
  
  <p>into this :</p>
  
  <pre><code>output &lt;- c("Théodore Agrippa d'Aubigné", "Vital d'Audiguier De La Menor")
  </code></pre>
  
  <p>The only words that should be modified are those that are all upper case.</p>
  
  <p><strong>Edit:</strong> </p>
  
  <p>An edge case, where first letter of sequence isn't in <code>[A-Z]</code>:</p>
  
  <pre><code>input &lt;- "Philippe Fabre d'ÉGLANTINE"
  </code></pre>