Break out json/json_lines codec.

This is a temporary fix to support both cases where uses are streaming newline delimited json messages (i.e. tcp, file) and parsing full json payloads (i.e. rabbitmq, redis). To solve this problem I've created a json and json_lines codecs that can be used for either scenario.

The json codec expects a full body of JSON and will attempt to parse it into an event as it.

The json_lines codec will buffer decoded data until a '\n' is hit, it will then emit an event.

In the future we will have a single JSON codec that will be able to parse while streaming, so either scenario can be handled.