Add skeleton Checkers class
Add Player stub
Add starter Board class
Initialize men, implement board duping and flipping
Fill out place_men in Board
Add Man class and overload bracket operators in Board
Improve man placement
Add board rendering
Make flipping and duping functions public, flip board every turn
Refactor man placement
Stagger the ranks of men
Add HumanPlayer stub
Make the game runnable with `ruby checkers.rb`
Make Board clear the screen before rendering
Wait for player input
Add InvalidMoveError stub
Improve parsing and make men move