-/* Try to move "monster" in random direction. On contact with other monster,
- * only bump. On contact with player, fight / reduce player's hitpoints,
- * and thereby potentially trigger the player's death. Update the log for any
- * contact action.
+/* Try to move "actor" one step in direction "d" and handle the consequences:
+ * either the move succeeds, or another actor is encountered and hit (which leads
+ * to its lifepoint decreasing by one and potentially its death), or the target
+ * square is not passable and the move fails.