Rejig formatting API. closes flarum/core#85

It works but it’s not the most pretty thing in the world. @franzliedke
Would be great if you could take a look at the whole formatting API and
work your magic on it sometime… my brain is fried!

framework/core/src/Api/Serializers/PostBasicSerializer.php

@@ -25,7 +25,7 @@ class PostBasicSerializer extends BaseSerializer
         ];
 
         if ($post->type === 'comment') {
-            $attributes['excerpt'] = str_limit($post->contentPlain, 200);
+            $attributes['contentHtml'] = $post->content_html;
         } else {
             $attributes['content'] = $post->content;
         }