Add getaddrinfo based DNS lookup implementation.

tests/0-dns.d

@@ -0,0 +1,31 @@
+/++ dub.sdl:
+	name "test"
+	dependency "eventcore" path=".."
++/
+module test;
+
+import eventcore.core;
+import std.stdio : writefln;
+
+bool s_done;
+
+void main()
+{
+	eventDriver.dns.lookupHost("example.org", (id, status, scope addrs) {
+		assert(status == DNSStatus.ok);
+		assert(addrs.length >= 1);
+		foreach (a; addrs) {
+			scope (failure) assert(false);
+			writefln("%s (%s)", a.toAddrString(), a.toServiceNameString());
+		}
+		s_done = true;
+		eventDriver.core.exit();
+	});
+
+	ExitReason er;
+	do er = eventDriver.core.processEvents();
+	while (er == ExitReason.idle);
+	//assert(er == ExitReason.outOfWaiters); // FIXME: see above
+	assert(s_done);
+	s_done = false;
+}