public Base(
string key,
string requestUrl,
Func<TRoot, T> rootToSingle,
Func<TRoot, IList<T>> rootToMultiple,
Func<T, string> itemToId)
{
client = ClientExtensions.CreateBillyClient(key);
//Todo: check for correctly formed url
this.requestUrl = requestUrl;
this.rootToSingle = rootToSingle;
this.rootToMultiple = rootToMultiple;
this.itemToId = itemToId;
}