Unhandled promise rejections

[evrys]

Sade is great, thanks!

I noticed that if my async handlers error out, then node exits with an UnhandledPromiseRejectionWarning but doesn't print the error message or stack trace or such. I think it'd be convenient if sade would catch these by default and print something, or give me an easy way to define an error handler (aside from manually wrapping each action).