* refactored code to eliminate Board and Position objects
* added a test for dropping a shape and when a row is completed
* added a test to showcase the behavior of a shape moving on the board
removed left and top attributes from Shape.
formatting
Started using the Command design pattern to abstract away the process of moving a Tetris shape on the board.
Created new MoveShapeAction command for rotating a Tetris shape clockwise.
Created a MoveShapeAction command for moving a Tetris shape down the board.
Got most of the features for playing Tetris working.