genmai.go
func (db *DB) CreateIndex(table interface{}, name string, names ...string) error {
	return db.createIndex(table, false, name, names...)
}
func (db *DB) CreateIndex(table interface{}, name string, names ...string) error {
	return db.createIndex(table, false, name, names...)
}
// CreateIndex creates the index into database.
// If table isn't direct/indirect struct, it returns error.