No support for multiple default indexers

Docu fails with an ArgumentException "An item with the same key has already been added." on PropertyGenerator when a class exposes more than one default indexer.

Example :

/// <summary>
/// Returns "Hey".
/// </summary>
/// <param name="index">The index</param>
/// <returns>"Hey"</returns>
public string this[int index]
{
    get { return "Hey"; }
}

/// <summary>
/// Returns "How".
/// </summary>
/// <param name="name">The name</param>
/// <returns>"How"</returns>
public string this[string name]
{
    get { return "How"; }
}