The puzzle generator and solver have been changed.
The theme now uses the engine from Python Sudoku
(http://pythonsudoku.sourceforge.net). This
provides a faster and more robust generator. It
also means that the difficulty levels mean
something. Previously, there wasn't much
difference between the difficulty levels. Now
there's a clear difference.
Games are now automatically saved as you go, so
they are restored when you restart. Cells are now
green until the ENTER button is pressed. This
gives a better clue about unentered cells. Deleted
cells are now handled correctly.
