Add a Shutdown method to server.
Add a Shutdown method to server.

Allow gracefull shutdown of a server.

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