/// <summary>
/// Add an ability of instantiating an instance of a class that has no default constructer.
/// </summary>
/// <typeparam name="T">Type of the object that is activated by this <paramref name="activator"/>.</typeparam>
/// <param name="activator">A delegate that creates an instance of <typeparamref name="T"/>.</param>
/// <example>
/// <code>
/// var serializer= new Serializer);
///
/// var yaml =
/// @"%YAML 1.2
/// ---
/// !System.Drawing.SolidBrush
/// Color: Red
/// ...
/// ";
///
/// SolidBrush b = null;
/// try {
/// b = (SolidBrush)serializer.Deserialize(yaml)[0];
/// } catch(MissingMethodException) {
/// // SolidBrush has no default constructor!
/// }
///
/// YamlNode.DefaultConfig.AddActivator<SolidBrush>(() => new SolidBrush(Color.Black));
///
/// // Now the serializer knows how to activate an instance of SolidBrush.
/// b = (SolidBrush)serializer.Deserialize(yaml)[0];
///
/// Assert.AreEqual(b.Color, Color.Red);
/// </code>
/// </example>
public void AddActivator <T>(Func <object> activator)
where T : class
{
Activator.Add <T>(activator);
}