A simple game of tic-tac-toe between two players that can be played through the command line!

Edit: 11/11/2019

• things I would like to improve: --General code cleanup and refactoring --reassess if 'board.rb' needs to require 'player.rb' --put attribute readers, writors, and accessors all in one line --Examine #game_over method so that the parameters are optional (right now I pass an argument of "" for one of the method calls)