Add onceDrain

[rnons]

Related to #15

It seems more common to use .once('drain', cb) than .on('drain', cb), at least on https://nodejs.org/dist/latest-v12.x/docs/api/stream.html, there are two .once('drain', cb) examples. Like

if (!stream.write(data)) {
    stream.once('drain', cb);
  } 

If you prefer .on('drain', cb) or both, I will update.

[hdgarrood]

I think the desire to bind to once indicates that we should rethink how we are binding to event emitters here actually. For each event, we often only provide a binding to on(evt, callback) but there's quite a lot of the node.js event emitter API which we aren't covering: https://nodejs.org/dist/latest-v12.x/docs/api/events.html. I would personally rather hold off on adding this and instead think about putting together a proper binding to EventEmitter, like https://github.com/joneshf/purescript-node-events/

[hdgarrood]

No, it probably shouldn't: I am saying that reproducing the whole EventEmitter API for every node API which uses events is undesirable.

[hdgarrood]

Potentially, yes. I think we should at least investigate that approach first.

[JordanMartinez]

Superceded by #49