This adds the `multipleResolves` event to track promises that resolve
more than once or that reject after resolving.

It is important to expose this to the user to make sure the
application runs as expected. Without such warnings it would be very
hard to debug these situations.

Fixes: nodejs/promises-debugging#8

This wraps the emit in a nextTick to have a individual context
instead of ending up in a potential promise catch handler. It also
renames the types to `resolve` and `reject` to be more neutral.
On top of that the message was removed to reflect the `type` change.