p-reflect

I like this module a lot! I think it would be even better if we were able to define possible resulting errors. I've adding backwards-compatible types for errors here, people might use this when they have known errors being returned by a function. At seam.co we have really error-heavy code, so we usually have types for all the errors that could be returned by a function. This might be one step towards getting all those errors nicely typed. Example code BEFORE ErrorType introduced: Example code after: I'm interested in comments but I think due to Typescript's all-or-nothing generics this feature might not be very helpful. (see how I have to include APIResponse in the AFTER type above?)

When I use p-settle to replace Promise.allSettled in my project for throttling, I want its return value can be adapted to the return of Promise.allSettled Fixes #8