Change JSON stream to always report data events instead of progress, follow strict stream semantics, support backpressure and improve error handling

[clue]

// old: all JSON streams use custom "progress" event
$stream = $client->eventsStream();
$stream->on('progress', function ($data) {
    var_dump($data);
});

// new: all streams use default "data" event
$stream = $client->eventsStream();
$stream->on('data', function ($data) {
    var_dump($data);
});

// new: stream follows stream semantics and supports stream composition
$stream = $client->eventsStream();
$stream->pipe($logger);