FEATURE: remove dependency of Redcarpet

PERF: cache fancy_title in topics table

New pure ruby implementation is far more flexible and easier to amend.

db/migrate/20150924022040_add_fancy_title_to_topic.rb

@@ -0,0 +1,5 @@
+class AddFancyTitleToTopic < ActiveRecord::Migration
+  def change
+    add_column :topics, :fancy_title, :string, limit: 400, null: true
+  end
+end