Fixed recursive solution: within Sudoku.copy, the Sudoku.found set is now copied instead of passed by reference!
Sorted recursive seeds; the depth-first search is now performed deterministically
Added Sudoku.devour, which consumes a child solution's attributes for self
Removed execute permissions, shebang, and `if __name__ == '__main__'` from sudoku/sudoku.py
Moved argparse into sudoku/sudoku.py's main()
Made additional verbose print levels (0=none, 1=prompt+final, 2=prompt+intermediate+final, 3=prompt+intermediate+final+seeds)
Cleaned up Sudoku.__init__
Capitalized State enumerations
Moved SIZE and DAT_DIRECTORY constants to test classes
Elevated test verbose level to 2; once all solution bugs and optimizations are finished, this will be lowered