Begun re-implementation of the AI engine

Implemented the following functions completely:
- ai_gamestate_new_initial
- ai_gamestate_new_child
- ai_gamestate_populate_children

Implemented the following functions partially:
- ai_gamestate_score
	This function needs to be far more complex in its calculation
	of the strength of a players position.

 On branch ai_restructure
	modified:   src/ai.c
	modified:   src/ai.h