Maquina de estados da cast

Pessoal, adicionei a funcionalidade de maquinas de estado da cast baseado na gem STATESMAN, sugestões são bem vindas. =)
O extra empty line eh a linha antes de fechar o end. 

```ruby
  transition from: :started, to: [:approved]
  transition from: :started, to: [:need_improvement]
  transition from: :started, to: [:not_approved]
  transition from: :approved, to: [:need_improvement]
  transition from: :need_improvement, to: [:approved]
  # <- linha problemática
end
```

E lembrando de sempre deixar a última linha em branco. =)

No final, deveria ficar assim:

```ruby
  transition from: :started, to: [:approved]
  transition from: :started, to: [:need_improvement]
  transition from: :started, to: [:not_approved]
  transition from: :approved, to: [:need_improvement]
  transition from: :need_improvement, to: [:approved]
  # <- linha problemática
end

```