Add tromp taylor rules

This adds a Game struct which becomes the new way to interface with the game. It also enabled to move a lot of stuff away from Board (which was becoming way too big).

In particular, get(u8, u8) is now only implemented on Game, which will translate to the correct get_coord(Coord) call, that way we have both the ease of get(u8, u8) and the non-repeating API in Board.

show() methods have been moved to Game as well, as I feel Board should only care about how to maintain the board state, and not how to display it.

For a similar reason, I moved the komi to Game, as Board doesn't need to know about it for any reason.

I didn't duplicate all the tests for the Game methods which are basically just calling the correct Board method, but added one for scoring, as komi is now added to the score by Game and not Board.