Reachedpos bbox expansion

The reachedpos_bbox_expansion spawnarg is meant for small AI like rats, mice, birds etc. It adjusts the [[bbox] around the target position of a goal, so that even AI with a small bounding box will be able to reach their target.

Without that adjustment, the might never get to their target as the approach it, but the target stays all the time outside the AIs box due to their turning not being fast enough. This causes the AI to reach a stable orbit around the target point and is usually not wha one wants.

The default is 0, and the value is in units. A value of 1..3 is usually sufficient. There should be no need to use this spawnarg on any entities in the editor.