Add error handlers

[eirslett]

It should be possible for applications to handle errors in the loggers, by adding e.g.

kafkaLogger.on('error', err => console.error('oops', err));

to the code. That means we need to forward the error events from the underlying implementations.

Another alternative is to let users provide their own scribe client or kafka client etc., and let them add error handling directly on their underlying client.

[CalebKing3]

This would be a really nice feature.