Add styling for new Remarkup highlighter

Summary: Adds some basic style to new !!Remarkup Highlighter!! Ref T5560

Test Plan: Wait for next diff.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T5560

Differential Revision: https://secure.phabricator.com/D14383

src/infrastructure/markup/PhabricatorMarkupEngine.php

@@ -510,6 +510,7 @@ final class PhabricatorMarkupEngine extends Phobject {
     $rules[] = new PhutilRemarkupItalicRule();
     $rules[] = new PhutilRemarkupDelRule();
     $rules[] = new PhutilRemarkupUnderlineRule();
+    $rules[] = new PhutilRemarkupHighlightRule();
 
     foreach (self::loadCustomInlineRules() as $rule) {
       $rules[] = $rule;