Support for Else conditions

[johnkievlan]

You know what would be nice? IfElse :)

[phatboyg]

Yeah, that might be cool.

[mattsve]

Meanwhile this extension method could be of use.

public static EventActivityBinder<TInstance, TData> IfThenElse<TInstance, TData>(
        this EventActivityBinder<TInstance, TData> binder,
        StateMachineCondition<TInstance, TData> condition,
        Func<EventActivityBinder<TInstance, TData>, EventActivityBinder<TInstance, TData>> thenActivityCallback,
        Func<EventActivityBinder<TInstance, TData>, EventActivityBinder<TInstance, TData>> elseActivityCallback)
        where TInstance : class
    {
        var result = false;
        return binder.If(context => result = condition(context), thenActivityCallback).If(_ => !result, elseActivityCallback); 
    }

[phatboyg]

Fixed by #55