Uncaught Promises should throw Exception

[davidbarratt]

I've noticed (#73) that uncaught errors do not throw exceptions, this can make debugging really difficult because there isn't an obvious reason of why a promise chain is breaking.

I believe in JavaScript, an uncaught promise error throws a fatal error, so I think throwing an exception (outside of the promise chain) for uncaught promises would be a good idea here.

[davidbarratt]

oh... well, all() does this but settle() does not.