horsegen: generate group -> skills relation

horsegen/skill.kk.template

@@ -92,6 +92,13 @@ pub fip fun skill/order2(a: skill, b: skill): order2<skill>
 pub fun skill/(==)(a: skill, b: skill): bool
   a.skill-id == b.skill-id
 
+// Get the skills in a skill group.
+pub fun skill-group/skills(g: skill-group): list<skill>
+  match g
+    {{- range $g := $.Groups }}
+    {{ kkenum $g.Name }} -> [ {{- range $s := index $.Related $g.ID }}{{ kkenum $s.Name }}{{ if ne $s.InheritID 0 }}-Inherit{{ end }}, {{ end }}]
+    {{- end }}
+
 // Get complete skill info.
 pub fun skill/detail(^s: skill): skill-detail
   match s