horse, cmd/horsegen: include tags in generated skills

Fixes #6.

skill.go

@@ -37,6 +37,7 @@ type Skill struct {
 	WitCheck    bool         `json:"wit_check"`
 	Activations []Activation `json:"activations"`
 	UniqueOwner string       `json:"unique_owner,omitzero"`
+	Tags        []uint16     `json:"tags"`
 	SPCost      int          `json:"sp_cost,omitzero"`
 	IconID      int          `json:"icon_id"`
 }