Add various difficulties of Sudoku

Sam,

Here are various difficulties of Sudoku, complete with metadata, description & visualization.  I've tested them all to ensure they have solutions (which they do).

Please can you accept all of them into the Base repository.  Please can you also add some of them to the Tiltyard rotations.  I suggest just grades 1 & 6H for now.  (If you added all 7 then approximately 1-in-9 active games on the Tiltyard would be a Sudoku variant - which would be a bit much.)

Thanks,

Andrew
Don't include this line; it automatically gets added by the ggp-repository server.