code: func munmap(db *DB) error {
  	if db.data == nil {
  		return nil
  	}
  
  	addr := (uintptr)(unsafe.Pointer(&db.data[0]))
  	if err := syscall.UnmapViewOfFile(addr); err != nil {
  		return os.NewSyscallError("UnmapViewOfFile", err)
  	}
  	return nil
  }
docs: // munmap unmaps a pointer from a file.
  // Based on: https://github.com/edsrzf/mmap-go