Add support for r53 as a nameserver

Hey, I'm sure your nameservers are great, but I'd really like to see this support using Route53. The API is fairly straight forward. Docs for AWS JS SDK are here: https://aws.amazon.com/sdk-for-javascript/

I'll consider it, although the current solution is just to use a wildcard subdomain. That should work just as well on Route53, even though the instructions for setup are Vercel-specific