expose enable_experimental_markdown_it

expose the site setting that enables the CommonMark engine

config/locales/server.en.yml

@@ -1024,6 +1024,7 @@ en:
     flag_sockpuppets: "If a new user replies to a topic from the same IP address as the new user who started the topic, flag both of their posts as potential spam."
 
     traditional_markdown_linebreaks: "Use traditional linebreaks in Markdown, which require two trailing spaces for a linebreak."
+    enable_experimental_markdown_it: "Enable the experimental markdown.it CommonMark engine, WARNING: some plugins may not work correctly"
     enable_markdown_typographer: "Use basic typography rules to improve text readability of paragraphs of text, replaces (c) (tm) etc, with symbols, reduces number of question marks and so on"
     allow_html_tables: "Allow tables to be entered in Markdown using HTML tags. TABLE, THEAD, TD, TR, TH will be whitelisted (requires full rebake on all old posts containing tables)"
     post_undo_action_window_mins: "Number of minutes users are allowed to undo recent actions on a post (like, flag, etc)."

config/site_settings.yml

@@ -491,7 +491,6 @@ posting:
     client: true
     default: 24
   enable_experimental_markdown_it:
-    hidden: true
     client: true
     default: false
   traditional_markdown_linebreaks: