Began promisification. #17

Finished promisification of Model.get(). #17

Promisified Model.getAll(). #17

Promisified Model#save. #17

Model#save integration test now passes. #17

Promisified Model#destroy. #17

Promisified Model#set. #17

Promisified Model#clear and Model#unset. #17

Promisified appropriate Connection methods. #17