v3.0.0

v3.0.0 brings better and more consistent error handling!

All errors from workers include the stack property, and any others (Firefox has some extra non-standard properties). Since normally stack traces are not sent from the worker to the main thread, instead we capture the stack trace in the worker and manually send it to the main thread.

Additionally, the callback passed to PromiseWorker.registerError will now recieve Error objects directly, rather than ErrorEvent objects or weird non-standard things that are kind of like ErrorEvent objects. This is a breaking change to the API, necessitating the new major version.