Consumer return code

[cody-greene]

A ConsumerHandler can return a status code for precise control of ack/nack behavior. An enum type is provided for convenience, but it's not necessary.

import {ConsumerStatus} from 'rabbitmq-client'

const sub = rabbit.createConsumer({
  queue: 'my-queue',
  requeue: false // behavior with exceptions
}, async (msg) => {
  // optionally return a status code
  // 0 or undefined - ack
  // 1              - nack(requeue=true)
  // 2              - nack(requeue=false)
  return ConsumerStatus.REQUEUE // 1
})

• [x] add some tests

[cody-greene]

fixes #20