FEATURE: site setting for Markdown typographer

It ships anyway with markdown.it so we might as well expose it

app/assets/javascripts/pretty-text/engines/discourse-markdown-it.js.es6

@@ -133,7 +133,7 @@ export function setup(opts, siteSettings, state) {
     breaks: opts.discourse.features.newline,
     xhtmlOut: false,
     linkify: true,
-    typographer: false
+    typographer: siteSettings.enable_markdown_typographer
   });
 
   setupHoister(opts.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_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)."
     must_approve_users: "Staff must approve all new user accounts before they are allowed to access the site. WARNING: enabling this for a live site will revoke access for existing non-staff users!"

config/site_settings.yml

@@ -497,6 +497,9 @@ posting:
   traditional_markdown_linebreaks:
     client: true
     default: false
+  enable_markdown_typographer:
+    client: true
+    default: false
   allow_html_tables:
     client: true
     default: false

spec/components/pretty_text_spec.rb

@@ -615,6 +615,13 @@ HTML
       expect(PrettyText.cook("# banana")).to include("\u25a0\u25a0")
     end
 
+    it 'supports typographer' do
+      SiteSetting.enable_markdown_typographer = true
+      expect(PrettyText.cook('(tm)')).to eq('<p>™</p>')
+      SiteSetting.enable_markdown_typographer = false
+      expect(PrettyText.cook('(tm)')).to eq('<p>(tm)</p>')
+    end
+
     it 'handles onebox correctly' do
       # we expect 2 oneboxes
       expect(PrettyText.cook("http://a.com\nhttp://b.com").split("onebox").length).to eq(3)