Release Candidate 3

Updated Sark's logic.  He will now try to cut off the player if nearby, so beware!

His logic routine goes in three steps:

1. Avoid crashing - On every move, Sark evaluates distance in front and to the sides.  If he's within a threshold of crash distance, and path to either side is clear, he will turn in direction of the player.  If only one side is clear up to crash distance threshold, he will take the turn.  If both turn options have less open distance than continuing ahead, he will move ahead and re-evaluate on the next move.
2. Boosting behavior - Sark cruises unless player is within a threshold distance of Sark.  While player & Sark have a medium proximity, Sark will boost.
3. Seeking behavior - When player & Sark are within a close proximity, Sark will turn towards player and attempt to cut them off.  This can lead to an exciting race around the game grid.