Add stream transformation use case example

[felixfbecker]

Add example explaining how the pipeline operator helps with transforming Iterable, AsyncIterable, Observable and streams.

[littledan]

This is great, but I have also heard from RxJS folks that pipeline would be a big improvement. Maybe we could get a code sample from there as well. Cc @benlesh

[felixfbecker]

Yup, I second that! The example I have:

Observable.from([1, 2, 3]).pipe(
  filter(x => x % 2 === 1),
  map(x => x + x)
)

would become this with the pipeline operator:

[1, 2, 3]
  |> filter(x => x % 2 === 1)
  |> map(x => x + x)

Do you think it's worth adding that too?

[littledan]

Yes, I think that'd be a good idea.

[benlesh]

Looks great. There is more I would say about this "pipeable operator" pattern in RxJS, since it's been in use for more than a year now. There are patterns that have emerged from this that make code more readable and testable than it would otherwise be if we used "dot-chained" operators. I'll try to add more in another PR soon.