Implement simple swarm mechanics

src/Dodge/LevelGen/SwarmPlacement.hs

@@ -6,7 +6,7 @@ import Dodge.Data
 import Dodge.LevelGen.Data
 import Dodge.Creature.State.Data
 
-import qualified Data.Set as S
+import qualified Data.IntSet as IS
 import Control.Lens
 
 swarmPS :: Int -> Point2 -> Float -> Creature -> Placement
@@ -22,4 +22,4 @@ setSwarm psts (PutCrit cr) w
   where
     cid = _crID cr
     theSwarm = Swarm swarmSet
-    swarmSet = S.fromList $ map (_crID . _unPutCrit) psts
+    swarmSet = IS.fromList $ map (_crID . _unPutCrit) psts