DialContext function

[stokito]

It would be great to add the code snippet from docs into library itself and cover with a test:

    DialContext: func(ctx context.Context, network string, addr string) (conn net.Conn, err error) {
        host, port, err := net.SplitHostPort(addr)
        if err != nil {
            return nil, err
        }
        ips, err := r.LookupHost(ctx, host)
        if err != nil {
            return nil, err
        }
        for _, ip := range ips {
            var dialer net.Dialer
            conn, err = dialer.DialContext(ctx, network, net.JoinHostPort(ip, port))
            if err == nil {
                break
            }
        }
        return
    },

So users may just use it direcly instead of copying from docs.

[stokito]

created a PR