Use standard callback signature

[pvorb]

You use function(result, err) as the signature for callbacks. Standard would be function(err, result). Nearly every other library uses callbacks this way and everyone would expect this lib to do the same.

[sbisbee]

Sorry, ignore my comment. I was still in the mindset for Sag-JS. :)

I'll still take a look at a few other libs though.

Thanks for submitting and using!