Is it possible to add `Switch` with selector parameter ?

[Thaina]

R3/src/R3/Operators/Switch.cs

Lines 2 to 10 in dc69078

	public static partial class ObservableExtensions
	{
	public static Observable<T> Switch<T>(this Observable<Observable<T>> sources)
	{
	return new Switch<T>(sources);
	}
	}

public static partial class ObservableExtensions
{
    public static Observable<T> Switch<T>(this Observable<Observable<T>> sources)
    {
        return new Switch<T>(sources);
    }

    public static Observable<TResult> Switch<TSource, TResult>(this Observable<TSource> source, Func<TSource, Observable<TResult>> selector)
    {
        return new Switch<TResult>(source.Select(selector));
    }
}

//// usage

Observable<User> UserDataListener;
var servantListeners = UserDataListener.Switch((userData) => { // change when user data has changed
    return userData.ServantIDs.Select((servantID) => DataBase.Table("Servant").Listen(servantID));
});

Advantage :

• cleaner API than Select->Switch for Observable chain
• can be find easier in autocomplete