Rebuild on top of the WHATWG Streams API

[jcranmer]

https://streams.spec.whatwg.org/

Unfortunately, the API is still not stable, nor is it actually implemented anywhere in the browser. This will constitute a major, breaking API deviation, but until the specification looks stable, I'll continue using the deliverData/deliverEOF combos I've been using.

(For bonus points: work out how to represent the handler of MimeParser with the streams API).

[lygstate]

What's the advantage of Streams API

[jcranmer]

The Streams API is what will (hopefully) come out naturally for things like file or socket I/O, and there are aspirations for being able to pass streams across worker boundaries.