Add 2x2 version of game

[luvarpt]

I would like to see 2x2 version of game (instead of numbers, collored circles, or faces, can be used). This will allow less aged players to enter sudoku world.

[Kamuno]

How would a "Hard" and "Easy" difficulty for this mode look like?

Or would you just remove the difficulty setting and call it something different?

[luvarpt]

My first idea would be to not support any difficulty settings. Would it hit some generalisation of code?

PS: My motivation for this enhancement proposal is that explaining non-square version of sudoku for ~5-year old child is a bit harder than for square sudoku. And easiest (in fact, the only one in app) is 9x9. This is a bit larger than many child in this age are able to process.

Sidenote: Simple cap from bottles can be used for 2x2 sudoku or also lego duplo bricks (in non-android world).