Sudoku class is defined in multiple files

[tinsmancb]

The repository should only have one version of the Sudoku class, which is capable of taking a board represented as a string and converting it to the "list of lists" representation. In general, if you are asked to modify a piece of code to add a feature, you should not copy the file to make a new version. If you are concerned about being able to revert your code to the original version, make a git branch!

[tinsmancb]

#4