Revision History
0.41   Sat Apr 15 12:00:00 2006 EDT
       - Enhanced solver and added tests for previously unsolvable puzzles:
          - 2 examples by Jean-Pierre Vidal
          - 6x6 puzzles, example from Brian Helterline
          - 16x16 puzzle from sudokusolver.com
          - 15x15 puzzle from sudoku.com's sud.exe
          - Several "evil" puzzles from WebSudoku
       - Allows \%config to be passed in, thanks to Brian Helterline
       - Added board validation
       - Bugs fixed:
          _get_or_set_square:
            Worked for squares but not rectangles.
             1. Had $x and $y reversed in accessing $self->{board}
             2. Was using $v_squares instead of $h_squares
          _array_to_text:
             3. Wasn't using a copy of $self->{board}, so printing
                a solution for debugging purposes screwed up later
                processing.
          _retry:
             4. Wasn't correctly copying and restoring $self->{board},
                so it wasn't able to brute force the solution to some
                hard problems.
0.10   Wed Jan 31 00:00:00 2006 EST
       - First Public Release