horse, cmd/horsegen: include tags in generated skills

Fixes #6.

cmd/horsegen/sql/skill.sql

@@ -87,7 +87,7 @@ SELECT
 	COALESCE(u.owner_id, iu.owner_id, 0) AS unique_owner_id,
 	COALESCE(u.name, iu.name, '') AS unique_owner,
 	d.icon_id,
-	ROW_NUMBER() OVER (ORDER BY d.id) - 1 AS "index"
+	d.tag_id
 FROM skill_data d
 	JOIN skill_names n ON d.id = n.id
 	LEFT JOIN skill_data ud ON d.unique_skill_id_1 = ud.id