public IRestResponse Batch(string listUrl, ListItems items, string action)
{
var body = items.Serialize();
var client = new RestClient(listUrl);
var request = new RestRequest("batch", Method.POST);
request.AddQueryParameter("type", action);
request.AddHeader("Accept", "application/xml");
request.AddHeader("Authorization", "OAuth " + this.accessToken.Token);
request.AddParameter("application/xml", body, ParameterType.RequestBody);
return(client.Execute(request));
}