public async Task DownloadPackageManifest()
        {
            // Downloads a package manifest (.nuspec)
            NuGetClient client = new NuGetClient("https://api.nuget.org/v3/index.json");

            string       packageId      = "Newtonsoft.Json";
            NuGetVersion packageVersion = new NuGetVersion("12.0.1");

            using (Stream manifestStream = await client.GetPackageManifestStreamAsync(packageId, packageVersion))
            {
                Console.WriteLine($"Downloaded package {packageId} {packageVersion}'s nuspec");
            }
        }