horsegen: generate sparks

horse/game-id.kk

@@ -46,6 +46,16 @@ pub struct race-thumbnail-id
 pub struct saddle-id
   game-id: game-id
 
+// Game ID for sparks,
+// i.e. succession factors.
+pub struct spark-id
+  game-id: game-id
+
+// Game ID for spark groups,
+// i.e. all rarities (star counts) of a single spark.
+pub struct spark-group-id
+  game-id: game-id
+
 // order2 comparison between any game ID types.
 pub inline fun order2(x: a, y: a, ?a/game-id: (a) -> game-id): order2<a>
   match x.game-id.cmp(y.game-id)