backup.go
func (db *DB) Backup(w io.Writer, since uint64) (uint64, error) {
	stream := db.NewStream()
	stream.LogPrefix = "DB.Backup"
	return stream.Backup(w, since)
}
func (db *DB) Backup(w io.Writer, since uint64) (uint64, error) {
	stream := db.NewStream()
	stream.LogPrefix = "DB.Backup"
	return stream.Backup(w, since)
}
// Backup is a wrapper function over Stream.Backup to generate full and incremental backups of the
// DB. For more control over how many goroutines are used to generate the backup, or if you wish to
// backup only a certain range of keys, use Stream.Backup directly.