add full response body (status, timeout, etc) queue.get("message_id)

`if` block is the same as `Queue#get_message(id)` method.

```ruby
def get_messages(options = {})
  # assume options is an id queue.get("010120141231")
  return get_message(options) if options.is_a?(String)

  resp = call_api_and_parse_response(:get, "/messages", options, false)
  process_messages(resp["messages"], options)
end
```