This is a rather big patch.
The Kigo::Engine was torn apart and refactored into several classes.
This provides some cleaner APIs and future extendability.

These are the new classes: Kigo::Score, Kigo::Player, Kigo::Move, Kigo::Stone.

This should be mostly self-explanatory but the comments where expanded too, to make relations clear.
The Kigo::Engine class got lifted even further, a lot of unused (and to be honest obscure) GTP command wrappers where removed.
Maybe some of them might be re-introduced when needed later.

This commit will cause new bugs because of it's size and the large code portion it touches.