Error handling + fixes

- easyamqp extends EventEmitter and emit error message from amqp connection
- unless "on" handler is registered error thrown
- queue options were overriden by {}
- more friendly initialization, backward compatible

coffeescript example:

```coffee
easyamqp = require 'easy-amqp'
amqp = easyamqp "amqp://..."
amqp.on 'error', (err) ->
  console.log err

amqp.queue('qname', {durable: 10, autoDelete: no})
.subscribe {ack: true}, (message, headers, deliveryInfo, m) ->
```