Support ParentResult API

[gurmitteotia]

It will be be useful if user can write following sytax

[WorkflowDescription("1.0")]
public class OrderWorkflow : Workflow
{
  public OrderWorkflow()
  {
    ScheduleLambda("ReserveOrder");
    ScheduleLambda("ChargeCustomer").AfterLambda("ReserveOrder")
       .WithInput(e=>new {Cost = e.ParentResult().OrderValue});
  }
}

At the moment user has to do

[WorkflowDescription("1.0")]
public class OrderWorkflow : Workflow
{
  public OrderWorkflow()
  {
    ScheduleLambda("ReserveOrder");
    ScheduleLambda("ChargeCustomer").AfterLambda("ReserveOrder")
       .WithInput(e=>new {Cost = e.ParentLambda().Result().OrderValue});
  }
}

Implementation Note:

• ParentResult() will throw exception if there are more than one eligible parents
• ParentResult() will throw exception when there are no parents
• ParentResult() will throw exception and the parent has successfully completed.

Eligible parents are- activity, lambda function and child workflow