horsegen: redesign character template

horse/character.kk

@@ -0,0 +1,17 @@
+module horse/character
+
+import horse/game-id
+
+pub struct character-detail
+  character-id: character-id
+  name: string
+
+pub fun detail(
+  c: character-id,
+  ?character/show: (character-id) -> string
+): character-detail
+  Character-detail(c, c.show)
+
+pub fun character-detail/show(d: character-detail): string
+  val Character-detail(Character-id(id), name) = d
+  name ++ " (ID " ++ id.show ++ ")"