changes:
Overlays now creates less temporary lists.
Falling no longer queues unsimulated atoms that wouldn't fall anyways (incl. LOs).
Pixel-shifted AO is now cached too.
Changed some references to get_map_cell() to macro equivalents in random maps.
Added smoothing hinting to the icon smoother, allowing for major performance improvements in common cases.
Space initialization no longer involves appearance churn (and is much faster as a result).
changes:
SSoverlays only creates the our_overlays and priority_overlays lists separately and when they're actually used. This should remove a lot of unused lists as priority_overlays is relatively unused.
SSoverlays is now FIFO.
SSoverlays now uses large Cut() operations instead of continuously truncating its processing list.
SSoverlays is no longer a processing subsystem.
Performance tweaks to add_overlay()
SSoverlays no longer tries to re-process atoms that have already forcibly compiled their overlays (like human-types).