skeletons added for all major methods of all classes
adds getter and setter methods to Board with validation
fixes error in the getter and setter methods for Board
Board#restock_pieces created, restructred board to have eight rows and four columns to better represent the possibilities of a checkers game
adds Board#connections
adds Board#empty?
completes Piece#slide_moves
This is a big commit that adds Piece#jump_moves as well as Piece#perform_slide and Piece#perform_jump
fixes bug in perform_jump
adds Board#render
adds a user interaction as well as the ability to take a sequence of moves at once
no longer allows players to slide if they have a jump available
adds winner and end game message