EventLoop.registerDns

Token registerDns(scope  const(char)[]  host,  DnsWatcherCallback callback,  CancelToken cancel =  CancelToken
         .invalid)

@trusted nothrow

`host`	Hostname to resolve.
`callback`	Callback invoked when resolution completes.
`cancel`	Optional cancellation token.

New watcher token on success, or Token.invalid with errno set.