Fix bottleneck when using confirms

Publishing msgs using confirms can create a situation where so many event listeners are registered that `exchange.removeListener` becomes a significant bottleneck (see https://gist.github.com/aheckmann/7762370)

Instead of relying on `EventEmitter`, this PR now registers a single error handler for the exchange and handle error disbursement manually.

Results of running the above gist as follows:

`> time DEBUG=amqp:* COUNT=30000 PREFETCH=0 BUCKET_SIZE=20000 node index.js`

before applying the fix:
```
real  1m22.216s
user  1m10.973s
sys 0m16.106s
```

after:
```
real  0m25.034s
user  0m14.082s
sys 0m15.153s
```

Also tried to make whitespace use more consistent throughout the project base on what seemed to be the predominant style.