A* implementation takes too much memory

[stephanemagnenat]

The current A* algorithm used in Map::pathfindPointToPoint uses a rich AStarAlgorithmPoint for each point's position. However, it should be able to run with a much lower overhead because both the move cost as well the direction can be inferred by a simple derivative of explored points.

[Giszmo]

When I start glob2, pmap reports a mem usage total of 671MB. That goes up to 690MB in a four player game with about 600 units. I say it's premature optimisation to spend time on this. Any PR that increases the code complexity to save some MB on big games would be a net negative.

[stephanemagnenat]

I never thought for this issue to be urgent, but I realized that while reading the code for something else, and thought that it was good to document that.