Increase streaming performance 50%+ percent.

If there's a need to decode JSONs in a streaming mode (where JSON objects are present in the stream one after each other), the with_trailer option allows returning the unconsumed part of the input along with the parsed terms.

In our tests it yielded 50% and more performance improvement compared to handling jiffy:decode() error exceptions and splitting the buffer along the provided invalid_trailing_data counter.

The pull includes EUnit test (15).