Add air slowdown

TODO.txt

@@ -19,7 +19,6 @@
   data file, try to somehow hack around it (maybe just convert it to an array in
   the end?) Maybe this: make a standalone C file with the string in it that
   when compiled and run outputs the array.
-- some kinda easteregg in menu or smt
 - culling is very slow now, it showed that distance bailout can accelerate it
   a lot, try to make a more accurate bailaout and see if it's faster (watch
   out for bugs due to false positives)
@@ -56,11 +55,6 @@
   - replay stretching works
   - replay with input not occuring for more that LCR_SETTING_GHOST_STEP
 - replay validation
-- make the racing module usable by itself, e.g. to allow making tools for
-  verifying replays etc., i.e. make the module measure time, count checkpoints
-  etc. DONE?
-- allow slowing down in air like in TM?
-  lower memory)
 - at the end check error handling, make sure the game handles garbage data in
   resource file etc.
 
@@ -76,6 +70,11 @@
 =========== HANDLED ==============
 
 - MAP4: one triangle in top section is missing!
+- allow slowing down in air like in TM?
+- some kinda easteregg in menu or smt
+- make the racing module usable by itself, e.g. to allow making tools for
+  verifying replays etc., i.e. make the module measure time, count checkpoints
+  etc. DONE?
 - add simple particle effects for grass/dirt/drift? Can be just a few squares
   animated from the projected backwheels.
 - FPS logging for optim