Cats typeclasses integration

[massimosiani]

Hi! Would it make sense to add a cats integration module, and provide derived instances for Show, Eq and Hash?
I could provide a PR if it makes sense.

[alexandru]

👍 go ahead

[massimosiani]

I implemented it here https://github.com/massimosiani/monix-newtypes-cats, if you have any advice.
I'll include the code in this repo.