Add a data model to store subscriptions.
Define permissions to subscribe or not.
Add method to unsubscribe.
Add a method to get the subscription between a user and a subscriptable resource.
Add interface to subscribe/unsubscribe.
Add an association to the subscribed user to the topics.
Spec the call to new reply notifier.
Define recipients of new reply notifications.
Add a method to generate proper good-looking recipient email.
Modify the API for a more direct style.
Mail a notification to subscribed users when someone post on a topic.
Configure SMTP mail server.
Add Delayed Job to send notifications in the background.
Merge branch 'user_can_subscribe_to_topics'
Add a useful README.