* Add migrations for subscriber_email column
* Add new schema
* Update relationships, specs, and factory
* Use unless index_exists? over if !index_exists?
* Fix typo in last fix for migration
* Rename authored_user_subscriptions
- to source_authored_user_subcriptions
* Add factory methods and specs
- UserSubscription.make
- UserSubscription.make_new
- Article.new_user_subscription
- Article.create_user_subscription
* Remove self and &
* Change make_new to build
* new_user_subscription --> build_user_subscription
* Come on, Travis
