Make scratch buffer size configurable (issue #2)

Controlled through the "log.line.scratch.size" property (default 4096)

Change-Id: I4a3f37d5b40bee4c33c7ba1bb4fa7a1c35bfb613
Log failed Kafka message deliveries (issue #1)

Controlled through "log.kafka.msg.error" property (default true)

Change-Id: I6dea3b13e38436597bc82dd048103c15e6c93c55
Provide some more detail when Kafka ..produce() fails.

Change-Id: Ia9bee394d14b4fcbe70dbe9cb1c4a46fc55edf30