Add lz4 compression

[rtreffer]

This patch may cause issues with kafka < 0.10.0 as it doesn't handle "broken" framing.
It should thus only be used with 0.10+.

[eapache]

Code looks fine. Two requests:

• Please add a test in message_test.go?
• Please guard this against the configured Kafka version so that if somebody tries to use it against an older Kafka version they get a useful error instead of weird misbehaviour.

[rtreffer]

config.Validate checks for versions < V0_10 and errs if LZ4 is enabled. Will add a message test later today.

[rtreffer]

@eapache encode / decode test, config check + tests.

[rtreffer]

Hm, the failed test looks like a false positive to me.

[eapache]

Ya, I've rerun it. Sometimes the broker just doesn't start properly on CI for some reason.

[eapache]

Thanks!