The client now emits errors on interesting events like connect, close, and error.
You are expected to listen for those events and act upon them. In particular, the
API has changed to that connect no longer takes a callback.

worker.start() no longer takes a flag to ignore the default tube. Instead you
can set 'ignoreDefault' in the options hash you pass to the worker constructor.

The worker no longer attempts to ignore the default tube if it's not watching
anything else.

Started implementing tests for the worker. This brings coverage up over
50% (which is pathetic, but it's a start) so I added coverage checking
to the test targets run by Travis CI.