Cleanups for Copy()
Cleanups for Copy()

Docs and slight code formatting issues.

skynet/dns,letsencrypt/dns,ErikDubbelboer/dns,tempbottle/dns,modulexcite/dns,miekg/dns,Git-Host/dns,AlexCheong/dns,jdef/dns,tsenart/dns,asergeyev/dns,bboreham/dns,michaelharo/dns,josephyzhou/dns,ym/go-dns,rolandshoemaker/dns,hugozhu/dns,janstk/dns,ezoic/dns,bragr/dns,curtiszimmerman/dns,skyportsystems/dns,Psiphon-Inc/dns,benbearchen/dns,cloudflare/dns,flebarbe/dns,FiloSottile/dns,jmhodges/dns