SImplify Board
Set beginner rules
Change constructor to simplify
A board has now a size! :)
The class of test for Board renamed as it should (xUnit style)
Add Position class
implement a nice toString method for error/exception
Use the king as example
Add a piece at a board position
Cannot add piece twice at the same position
Make a specific error

Because we will have a lot more to manage
Check for position existence in board
Check for position validation on board
addPiece return this to allow method chaining
Use a generic Piece instead of a king