If grid.HumanSolve returns nil in grid.Difficulty, panic immediately (which isn't that much more useful, but is a bit more clear what's going on). Related to #134.
If grid.HumanSolve returns nil in grid.Difficulty, panic immediately (which isn't that much more useful, but is a bit more clear what's going on). Related to #134.

jkomoros/sudoku,jkomoros/sudoku,jkomoros/sudoku