Add markdown cache columns to the database, but don't use them yet

This commit adds a number of _html columns and, with the exception of Note,
starts updating them whenever the content of their partner fields changes.

Note has a collision with the note_html attr_accessor; that will be fixed later

A background worker for clearing these cache columns is also introduced - use
`rake cache:clear` to set it off. You can clear the database or Redis caches
separately by running `rake cache:clear:db` or `rake cache:clear:redis`,
respectively.

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/banzai.rb b/lib/banzai.rb
index 9ebe379f454..35ca234c1ba 100644
--- a/lib/banzai.rb
+++ b/lib/banzai.rb
@@ -3,6 +3,10 @@ module Banzai
     Renderer.render(text, context)
   end
 
+  def self.render_field(object, field)
+    Renderer.render_field(object, field)
+  end
+
   def self.cache_collection_render(texts_and_contexts)
     Renderer.cache_collection_render(texts_and_contexts)
   end