public static async Task ExecuteAsync()
        {
            var client = new HttpClient();
            //client.DefaultRequestVersion = new Version(2, 0); // boost a bit with http2

            var service = new ContactsService(client);

            var contact = await service.GetContactAsync(4123);

            Console.WriteLine($"{contact.EmailAdress}");

            var response = await service.DownloadAsync("234");

            await service.UpdateContactAsync(contact);

            var start = DateTime.Now;
            var tasks = new List <Task>();

            for (int i = 0; i < 500; i++)
            {
                var task = Task.Run(async() =>
                {
                    Console.Write(">");
                    var list = await service.GetAllAsync();
                    Console.Write("<");
                });
                tasks.Add(task);
            }
            ;

            Task.WaitAll(tasks.ToArray());

            Console.WriteLine($"{DateTime.Now - start}");
        }