Support async iteration

[timwis]

Hello! I've noticed that streams created with this library do not support async iteration. This appears to be because it depends on readable-stream v2.x.x, and Symbol.asyncIterator was added to that library in v3.x.x, when it started supporting Node v10. I noticed in #21 that there was reluctance to upgrade to readable-stream v3.x.x, but that was more than a year and a half ago.

Would you be open to a PR that updates the dependency? Or does that issue still remain? Alternatively, any suggestions for how I might support async iteration in streams created by this library?

[seriousme]

Async iteration can easily be fixed by:

const legacyStream = from2([opts], read)
const modernStream = (new Readable({objectMode:true}).wrap(legacyStream))

See also: #24