feat(asyncify): adds asyncify and asyncifyErrback

[mattpodwysocki]

Description:

Adds the asyncify and asyncifyErrback to bind to callbacks to support regular callbacks and node style errBack callbacks to be bound to AsyncIterable.

Related issue (if exists):

[leebyron]

I think these are only likely to be marginally valuable since awaiting a single value is typically better modeled as a Promise instead of an AsyncIter, and there are already tools out there to convert a node callback to a Promise (and tools to convert a Promise to an AsyncIter that resolves once). - you should make sure documentation for this clearly indicates that the AsyncIter will close after the callback is called once, since I think most would be surprised by that behavior (this is a multi-value streaming library after all).

I believe the tweet motivating this change was looking for conversion from a callback that's intended to be called multiple times into an AsyncIter that resolves multiple values - it would be great to have a utility for doing that.