Consumer: wait for messages by default

Prior to this change min_bytes was 0 by default which causes the fetch
command to unexpectedly return regardless of the max_wait_ms setting.

Also, fixed options for PartitionConsumer#fetch to expect max_wait_ms
and not max_wait.
Merge pull request #48 from bpot/bp/consumer_sleep

Consumer: block for messages by default
Run integration specs on travis-ci
Fix typo