Import of the fltk example application sudoku that can generate sudoku

Import of the fltk example application sudoku that can generate sudoku
games and solve them.

Sudoku (pronounced soo-dough-coo with the emphasis on the first syllable)
is a simple number-based puzzle/game played on a 9x9 grid that is divided
into 3x3 subgrids. The goal is to enter a number from 1 to 9 in each cell
so that each number appears only once in each column and row. In addition,
each 3x3 subgrid may only contain one of each number.