Way to process selected objects from the input JSON stream

It is common task to parse out some JSON object from the input stream to process it somehow. There is [JsonPath] (http://goessner.net/articles/JsonPath/), but I propose to do it in other way.
SubsetConsumer class calls function consume() for each complete object from the stream. User's code can whether "consume" that object or not. See test for use cases tests/Listener/SubsetConsumerTest.php.