RED single move rendered.
GREEN
REFACTOR DRY the BoardRenderer instantiation.
REFACTOR parameterise _print_row().
RED cope with two moves.
GREEN
REFACTOR improve sanity of rendering rows.
RED test full board render.
GREEN
REFACTOR roll back board-rendering loop.
REFACTOR simplify _print_row() (row-size--agnostic).
REFACTOR use slicing in board render().
REFACTOR named magic numbers.
REFACTOR extracted method for updating cells.
REFACTOR extract number of players field.
REFACTOR extract magic numbers.
REFACTOR extract player numbers as fields.
REFACTOR pull out row size and row-starting cells as fields.
REFACTOR extract board size magic number.
REFACTOR extract methods to set up the cells and to print the board.