Module board
Source - Bag
 - An implementation of the 7-bag randomizer. Pieces are drawn from a bag of 7 pieces,
and when the bag is empty, a new bag is created and shuffled.
 - Board
 - The board is represented as a 2D array of u8, where PieceColor::Empty is an empty cell and any other value is a piece.
 - CurrentPiece
 - The current piece in the game, that is, a piece that is currently being moved by the player and has not
been committed to the board yet.
 
- clear_lines
 - Clears any lines that are full and moves the lines above down.
 - draw_piece
 - Draws the piece on the board.
 - draw_tracer
 - Draws the tracer piece on the board.
 - remove_piece
 - Removes the piece from the board.
 - remove_tracer
 - Removes the tracer from the board.