implement fully recursive stub resolver

[lanrat]

Do not require an external fully recursive resolver to identify all NS/A/AAAA records for domains and zones by implementing one as a DNS client in go.

Possible starting points?
https://godoc.org/github.com/domainr/dnsr
https://github.com/zmap/zdns

[lanrat]

cname example: https://github.com/semihalev/sdns/blob/master/middleware/resolver/resolver.go#L216

[lanrat]

other docs/examples:

https://gist.github.com/andrewtj/056ed6225898d652288f0d416eb3cc3f

https://github.com/semihalev/sdns/blob/master/middleware/resolver/resolver.go#L143

[lanrat]

Another source for a fully recursive resolver: https://github.com/zmap/zdns

[lanrat]

another option: https://github.com/projectdiscovery/tinydns