Tweaks to kakuro_cell to support comparison and remove implicit construction
Overload some operators in preparation for pimpling
Able to load variable sized grids
Add _width and _height to state of some kakuro objects
On kakuro_rows this is fixed on construction
On kakuro_grids this is variable untill a row has been added, after that it's fixed.
Kakuro_grids can only consist of rows that are the same width and are complete
Validations on kakuro_loader to ensure loading only works on wellformed data
enable kakuro solving to function when clues appear mid column or row