[math-fun] Rook 3×4 and 4×4 graphs are graceful

Both found by nickgard Rook move differences give all values 1 to 30. 0 1 9 30 16 29 2 19 22 3 27 7 Rook move differences give all values 1 to 48. 0 1 23 47 19 44 9 2 37 42 3 11 48 4 36 32 --Ed Pegg Jr