feature/rds

[ana0]

Addressed PR comments, except for deletion_protection .. looks like it was added to terraform only really recently (it's not in my version yet, for example) .. https://github.com/terraform-providers/terraform-provider-aws/issues/6008

Do we all want to upgrade?

[d-xo]

I'm fine with requiring the latest version of terraform.

[edzillion]

Problems applying this due to problems with CIDR block allocation.

Following this article: https://medium.com/@yaofei/aws-cidr-using-cloudformation-and-terraform-4f10bd86dbca