Add missing properties information for exchange.publish documentation

There are some properties used for exchange.publish but not listed in the doc (like userId, appId. etc..). These are written here: http://www.rabbitmq.com/resources/specs/amqp0-9-1.pdf under 1.8.1. Property and Method Summary, page 42. Node-amqp accept these as key-value for the options object. 

It's already supported by node-amqp but now written in the docs. This commit just add those missing information.