added ability to save and load games
changed binary structure to use Game class
added getters for game instance vars
added color to important indications
added to_a method
added additional case checks to knight spec
fixed knight movement so it can block for the king in check
added ability to save game state to the binary
added 'are you sure' when quitting
updated readme
added checking that a move is [rank][file] [rank][file]
updated readme
corrected issue with rank and file checking preventing player from making moves
added method for the board to see if a piece can be promoted
added ability to promote pieces in the binary