Implement WritableStream

[nickshanks]

I would like it if Oboe implemented WritableStream too.

Instead of oboe(readableStream.pipe(something).pipe(somethingElse)).on('done', (json) => …);
We could have readableStream.pipe(something).pipe(somethingElse).pipe(oboe()).on('finish', (json) => …);

It would fit into the left-to-right reading of data pipelining, and use the standard Writable event names.