fixing del docs

[arschles]

replaces #59

cc/ @sunloverz

[sunloverz]

Could you resolve conflicts and I will merge?

[alex-litvak]

I think it is better to create the 'options' variable and mention that it can contain reservation_id and subscriber_name if needed (will be clearer):
var options = {};
queue.del(message_id, options, function(error, body) {});