/// <summary> Attaches the callback to fire when progress is reported.
///
/// This is usually called at the beginning of the task.
/// Returns the current progress task, so that methods may be chained.
/// </summary>
/// <param name="callback">Attach a callback to the ProgressChanged event</param>
public ProgressEnumerator <T> SetCallback(ProgressChangedCallback callback)
{
progress.SetCallback(callback);
return(this);
}