Cleanup creature update slightly, add show instance for impulses

src/Dodge/Creature/Impulse.hs

@@ -17,7 +17,8 @@ import System.Random
 import Data.Bifunctor
 --import Data.Maybe
 
-impulsiveAI :: (World -> Creature -> Creature)
+impulsiveAI 
+    :: (World -> Creature -> Creature) -- | internal creature update
     -> Creature
     -> World
     -> (World -> World , Creature)
@@ -61,7 +62,7 @@ followImpulse cr w imp = case imp of
         _        -> crup cr
     ImpulseUseAheadPos f -> followImpulse cr w (f (_crPos cr +.+ 20 *.* unitVectorAtAngle (_crDir cr)))
     MvForward       -> crup $ crMvForward speed cr
-    MvTurnToward p  -> crup 
+    MvTurnToward p  -> crup
         $ creatureTurnToward p (turnRad $ safeAngleVV (p -.- cpos) (unitVectorAtAngle cdir)) cr
   where
     crup = (id,)