+Empty IAction
+Evaluate method to interface
+Empty Adder, not-implemented
+Evaluate implementation for Adder
+Empty Calculator
+Ability to Add to Calculator
+Empty Subtractor, not Implemented
Implement Evaluate in Subtractor
+Ability to Subtract to Calculator
Renaming IAction to IOperation
F Handle IOperation rename in Adder
F Handle IOperation rename in Calculator
F Handle IOperation rename in Subtractor for real