Feature Request: Set Riddle Difficulty about sudoku

[sfuhrm]

A good idea. For the machine all sudokus are equally difficult and the algorithm doesn't care.
There are approaches trying to guess the difficulty for humans, i.e. as described here.
Current idea: The current approach's degree of freedom matrix would get an accompanying human score matrix.

May be the first step is to have a solver that can assign a score.

Suggestions, drafts and pull requests welcome.

[Lemkinator]

It would also be nice if the size could be variable to solve for example 4x4 or 16x16 sudokus...
Regarding the riddle difficulty, one approach would be to set the amount of empty fields... (not the best approach, but propably easier to implement)...