A broad refactor 

After [thinking more in depth](https://github.com/amoslanka/notify/issues/1#issuecomment-64528626) about some naming and some upcoming architectural needs, this is a refactor that will change quite a bit of the core of the library. 

- [x] Rename NotificationType to Notification
- [x] Rename Notification model to Notify::Message
- [x] Rename Notification::Delivery to Notify::Delivery
- [x] Rename Ruleset to Strategy
- [x] Move creation logic to Notification
- [x] Handle Notification's heavy lifting of creating and delivering to delegate objects
- [ ] Notification presenter methods