…f returning a byte array

Introduce a new (internal) StreamingEncoder interface to be implemented by Encoders that supports writing directly into the output stream instead of returning their results as a byte array.

Update both the AbstractLogstashTcpSocketAppender and the CompositeJsonEncoder to support this new interface. This should hoppefully reduce the amount of short-lived byte arrays created for each log event.

See logfellow#461 for more information.

… ByteArrayOutputStream for every log event