NGINX Integration with Cloud Autoscaling

nginx-asg-sync allows [NGINX Plus](https://www.nginx.com/products/) to discover instances (virtual machines) of a
scaling group of a cloud provider. The following providers are supported:

- AWS [Auto Scaling groups](http://docs.aws.amazon.com/autoscaling/latest/userguide/WhatIsAutoScaling.html)
- Azure [Virtual Machine Scale Sets](https://docs.microsoft.com/en-us/azure/virtual-machine-scale-sets/)

When the number of instances changes, nginx-asg-sync adds the new instances to the NGINX Plus configuration and removes
the terminated ones.