switched to future{...} to prevent deadlocks
Merge remote-tracking branch 'origin/feature/kafka_0.8' into feature/kafka_0.8

Conflicts:
	storehaus-kafka-08/src/main/scala/com/twitter/storehaus/kafka/KafkaAvroSink.scala
	storehaus-kafka-08/src/main/scala/com/twitter/storehaus/kafka/KafkaSink.scala
	storehaus-kafka-08/src/main/scala/com/twitter/storehaus/kafka/KafkaStore.scala
	storehaus-kafka-08/src/test/scala/com/twitter/storehaus/kafka/KafkaContext.scala