SudokuShow - This program creates and displays Sudoku puzzles, and allows the user to fill in the puzzle and to check the solution.
    Here's how you play:    Click on the white squares to change them.  When you do, a window will come up showing you the numbers 1 through 9.
                            Pick the number you want and it will appear in the box.
                            Click File->Check to see if you've got the right answer.
                            Remember, the rules of Sudoku are: Each column, row, and 3x3 box must have the numbers 1 through 9 exactly once.
                            You can create a new puzzle by selecting File->Generate.  You will be asked what difficulty you want.
                            
Documentation:

    USAGE: perl SudokuShow.pl [-t] <Seed file>
    [-t]: include this switch to activate testing mode, where tests will be run and their results displayed.
    [Seed file]: the name of the file containing the seed sudokus.  If omitted, it defaults to "Seeds.txt".
    The seed file must be organized as follows:
        *The file must be at least 84 lines long.  Any lines past 84 will be ignored.
        *The file is organized in 4 blocks of 21 lines.
        *Each block represents a Sudoku/Answer combination of increasing difficulty.  The first block is designated easy, then medium, hard, and very hard.
        *The first, second, and twelfth line of each block are reserved for comments or headers and are ignored.
        *The rest of the lines in each block must each contain 9 numbers between 0 and 9, separated by a single space.
        *Lines 3 through 11 represent the puzzle, with 0 signifying a blank.
        *Lines 13 through 21 represent the solution, with no 0s.


    Version History:
        Since 1.0.1 Release:
            * The code has been further cleaned up and tweaked to conform to API specifications.
            * The documentation has been further refined and corrected.
        Since 1.0.0 Release:
            * Testing has been added.
            * The documentation has been refined, corrected, and expanded.
            * The code has been cleaned up.
        Since 0.5.0 Beta:
            * More inline documentation has been added, as well as an inline API.
            * Old unused code has been removed.
            * Argument passing has been streamlined.
        Since 0.4.1 Beta:
            * A new difficulty, Very Hard, has been added.
        Since 0.4.0 Beta:
            * The program now reads multiple sets of puzzles and answers from a single file.
            * The program now uses different seeds based on the selected difficulty.
            * The program now refreshes the puzzle state between regenerations.
        Since 0.3.0 Beta:
            * The program now reads both the puzzle and solution from a single file.
        Since 0.2.0 Beta:
            * The generator function now regenerates the puzzle with a new permutation.
        Since 0.1.2 Beta:
            * Shuffle and randomize functions have been added to allow for permuting of puzzles.
        Since 0.1.1 Beta:
            * The fixed cells are now also buttons, but with no functions associated, making them the same size as the blanks.
        Since 0.1.0 Beta:
            * The buttons are now a different color from the labels.
            * The buttons now bring up a dialog that allows editing.
            * The check function now runs when expected and displays a dialog.
            * Because cell altering and puzzle checking are now operational, it is now possible to solve puzzles.
            * A generate option has been added to the menu.
        Since 0.0.4 Alpha:
            * The program now reads a puzzle and an answer from two text files specified as arguments.
            * The program displays blanks as buttons.
            * The program can check the puzzle against the answer for correctness.
        Since 0.0.3 Alpha:
            * The program now looks for the file sudoku.txt and reads a completed sudoku from it.
            * The program also displays that sudoku as a grid of labels in the main window.
        Since 0.0.1 Alpha:
            * The program displays a window with file and help menus.
            * The file menu contains a working quit button.
            * The help menu contains version and about windows that open descriptive dialog boxes.

    API:
    sub build_window        # Usage: build_window().  It extracts a sudoku from the seed matrix based on the global difficulty, then sets up the window and calls for the buttons and the menubar.
    sub build_box           # Usage: build_box(Display value, position y, position x).  Creates a button displaying the value, or blank and editable if value is zero, then attaches it to the grid at [y][x].
    sub build_menubar       # Usage: build_menubar().  It assembles a help and file menu and attaches them to the SudokuShow window.
    sub check               # Usage: check().  Checks the global Sudoku matrix against the global Answer matrix, and informs the player of the result.
    sub alter               # Usage: alter(New value, index i, index j).  Replaces the [i][j] element of the Sudoku global matrix with the provided value.
    sub generate            # Usage: generate().  Queries the user for the difficulty level of the new puzzle and then creates that puzzle, deleting the current one.
    sub shuffle             # Usage: shuffle().  Randomly permutes the global Sudoku and answer matrixes in unison to produce a valid new puzzle.
    sub randomize           # Usage: randomize(Array reference).  Randomly permutes the passed array in its current location.