From: Anne van Kesteren [ann...@annevk.nl]
> Stream.prototype.readType takes an enumerated string value which is
> "arraybuffer" (default) or "text".
> Stream.prototype.read returns a promise fulfilled with the type of value
> requested.
I believe this is somewhat similar to how Node streams have settled. Their API
is that you call `stream.setEncoding('utf-8')` and then calling `.read(n)` will
return a string of at most n characters. By default, there is no encoding set,
and calling `.read(n)` will return n bytes in a buffer.
In this way, the encoding is a stateful aspect of the stream itself. I don't
think there's a way to get around this, without ending up with dangling
half-character bytes hanging around.
