provide generators à la scalacheck

[MasseGuillaume]

Are these hardcoded? If you're not already using scalacheck and Arbitrary/Gen, then you could allow me to create an instance of Arbitrary[List[Int]] and use that... implicits with low priority defaults seem like a good way to allow more customization without adding more buttons.

https://github.com/CodeBrew-io/Issues/issues/5