Message timestamp support

[andimiller]

Kafka added timestamps to it's messages back some time around 0.10.x

It's handy to have these so the server can compact more reliably, and so KSQL doesn't throw up when reading messages produced by fs2-kafka.

Useful links:
The original KIP
The JIRA ticket
The github PR with the change

[pchlupacek]

Not sure if we would be able to do so before fs2 1.0.0 version. But Intention is to add support and tests for all major releases of kafka, possibly dropping 0.9/0.8 support. perhaps that will get in 0.4.1 release, which hopefully will be in month or two.