feat: Add Next and Previous in Tag

fields.go

@@ -78,12 +78,20 @@ type CommitGroup struct {
 	Commits  []*Commit
 }
 
-// Tag ...
-type Tag struct {
+// RelateTag ...
+type RelateTag struct {
 	Name string
 	Date time.Time
 }
 
+// Tag ...
+type Tag struct {
+	Name     string
+	Date     time.Time
+	Next     *RelateTag
+	Previous *RelateTag
+}
+
 // Version ...
 type Version struct {
 	Tag           *Tag