code: func (lz *Lz4) Compress(in io.Reader, out io.Writer) error {
  	w := lz4.NewWriter(out)
  	w.Header.CompressionLevel = lz.CompressionLevel
  	defer w.Close()
  	_, err := io.Copy(w, in)
  	return err
  }
docs: // Compress reads in, compresses it, and writes it to out.