rns the minimum element in <code>self</code> or <code>nil</code> if the sequence is empty.</p>

<p><strong>Complexity:</strong> O(<code>elements.count</code>).</p>

<p><strong>Requires:</strong> <code>isOrderedBefore</code> is a
  <a href="http://en.wikipedia.org/wiki/Strict_weak_order#Strict_weak_orderings">strict weak ordering</a>
  over <code>self</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func minElement(@noescape isOrderedBefore: (Element, Element) throws -&gt; Bool) ret