Add superscript/strikethrough flags on markdown

app/javascript/styles/mastodon/rich_text.scss

@@ -87,6 +87,10 @@
     color: $ui-secondary-color;
     padding: 0 2px;
   }
+
+  sup {
+    vertical-align: super;
+  }
 }
 
 .reply-indicator__content {

app/lib/text_formatter.rb

@@ -174,6 +174,8 @@ class TextFormatter
         underline: true,
         disable_indented_code_blocks: false,
         fenced_code_blocks: true,
+        strikethrough: true,
+        superscript: true,
         highlight: false
       )
     @markdown.render(html)