tuidoku VS ltsim

By pencil mode I mean the ability to annotate the board like you would do on normal paper. [Here, 2nd screenshot](https://github.com/flyingpeakock/tuidoku#screenshots) you can see what I mean. If you need such feature I suggest you to use in fact [tuidoku](https://github.com/flyingpeakock/tuidoku). I'm not sure if I'll implement it in sku.

in modern C++ you should avoid raw pointers (or let's say it differently: you have to have a valid reason to use them) and use a smart version provided by the std library, usually std::unique_ptr is what you're searching for. Also if I'm not wrong, the memory assigned to "win" is never released because the dtor body is empty (that's the perfect example that explains why you want to use a smart pointer).If after switching from raw pointer to a smart pointer you still need to write explicitly a destructor, you should be conform to the rule of 5 (provide copy ctor and assignment, and move ctor and assignment as well).