Post json-response and content-type-jsonresponse.

attend-event-ajax is next
Finishing ajax
Finishing error-pages and render-controller
Merge remote-tracking branch 'origin/episode2' into episode2

* origin/episode2:
  Updating screencast version
  Fixing build errors
  Attempting to play with the version number
  updated video image
Merge branch 'episode3' into episode2

* episode3:
  this bake sale is going to be off the hook
  ship it
  winning
  judo chop!
  read to avoid sadness and regret
  beautiful slugs!
  eww slugs
Merge branch 'episode2'

* episode2:
  Finishing error-pages and render-controller
  Finishing ajax
  Post json-response and content-type-jsonresponse.