Added next_pos function to Grid. Added heuristic_distance estimator to RunnerPlayer.
Added surrounding_valid_coords to Grid, added AStarNode class
Implemented a-star pathfinding algorithm.
Disable chaser for now. Added visualisation of A* algorithm
Added walls
Added walls
Added readme
Updated readme
Added events. Streamlined A* algorithm.
Made the A* code character agnostic. Set up chaser to use it as well.
Added a 'target_gone' check to see if the object we're routing to is still there or not
Code tidying
Merge branch 'feature/a-star' into develop