Brute force and optimized Sudoku solver.

Inspired by the Python script from Peter Norvig (norvig.com/sudoku.html)

The brute force solution simple iterates over all cell to find a working solution.

The SudokuBoard2 uses search/eliminate, and uses int arrays and bitmasking to improve performance.

Update 10/2/2020: Added Suguru / Tectonic solver.