DNS class abstract

Main entry point to Node's "dns" module functionality.

Instead of using this class directly consider dns object.

Usage:

import 'package:node_interop/dns.dart';

void main() {
  var options = new DNSLookupOptions(all: true, verbatim: true);
  void lookupHandler(error, List<DNSAddress> addresses) {
    console.log(addresses);
  }
  dns.lookup('google.com', options, allowInterop(lookupHandler));
}