This is a bare-bones program that opens a basic TCP/IP socket to a
particular non-encrypted web server, on port 80, sends a hardcoded
HTTP/1.1 request, dumps the response, and should disconnect when the
remote side closes the connection. All necessary callbacks for this are
installed. The main loop() starts a connection attempt every 20 seconds,
and otherwise just outputs stars to show it is still running while the
AsyncClient does its thing.