title: Include html text inside a Drupal 8 generated link
body: <p>I have a hard time to style a link via the Drupal 8 render structure.
  This link needs to be displayed in my custom module:</p>
  
  <pre><code>$add_link = \Drupal::l('&lt;i class="fa fa-cog"&gt;&lt;/i&gt;' . t('Add new project'), $url);
  </code></pre>
  
  <p>So between de  tags I want a Font awesome icon in front of the text.
  But Drupal print all html out as readable text.</p>
  
  <p>I also notice that the l() function is deprecated in Drupal 8.
  So what is the best way to do this in the Drupal 8 render structure?</p>