Knight's Tour: Non-square board

[Steffan Sølvsten]

With #27 we also want that the value of N is treated a little bit differently.

Board Size	2x2	2x3	3x4	4x4	4x5	5x6	6x6	6x7	7x8	8x8

Which means the board size is

const int square_size = 2 * (N / 3);

const int N_rows = square_size + (N % 3 > 0) + (N % 3 > 1);
const int N_cols = square_size + (N % 3 > 1);