Notable changes since 3.2:
- Added mailer previews feature based on 37 Signals mail_view
gem.
- Instrument the generation of Action Mailer messages. The time it
takes to generate a message is written to the log.
- link_to and url_for generate absolute URLs by default in templates,
it is no longer needed to pass only_path: false.
- Introduced deliver_later which enqueues a job on the application's
queue to deliver emails asynchronously.
- Added the show_previews configuration option for enabling mailer
previews outside of the development environment.
