Added Pawn.class
Added SlidingPiece#moves
Removed #move_dirs from SlidingPiece down each of it's subclasses (Bishop, Rook, Queen)
Added some more notes to methods
Begin writing SlidingPiece#moves
Implemented Piece#add_positions and modified SlidingPiece#moves
Implemented Piece#out_of_bound? method
Implemented Board#at and Board#empty? methods
Add :color to Piece
Finish SlidingPiece#moves method
Finished King#moves
Finished King#moves and Knight#moves methods
Refactored SteppingPiece#moves to take King# or Knight#get_diffs
Separated chess.rb into separate class files; chess.rb no longer main file
Finished Pawn#get_diffs method and implemented Pawn#moves
Setup Board#initialize method
Added Board#setup_pieces method
Added Board#in_check?, added #in_check? helper methods
Finished the Board#in_check? method