#Sudoku Solver

I like playing sudoku so I figured I'd try programming it.

##The Idea The program uses a min-heap to organize the boxes by the number of possible answers. Boxes with only one possible answer, singletons, are popped off the min-heap and used to simplify the remaining boxes. If all singletons are removed and there are still unsolved boxes, uses a depth-first search to find the answer.

##To-Do Try and work in other simplifications besides singleton propagation. For example, two boxes with two identical numbers as their only possible answers.