Add `wakeup` to Consumer as in Java Client

Java client has [wakeup()](https://kafka.apache.org/0101/javadoc/org/apache/kafka/clients/consumer/KafkaConsumer.html#wakeup()) functions that can be used to break out of a `poll()` and can be called from another thread. It's needed for some unique cases like the process pool processing example, where we have 1 consumer and a pool of workers.