compress.go
func AppendGzipBytesLevel(dst, src []byte, level int) []byte {
	w := &byteSliceWriter{dst}
	WriteGzipLevel(w, src, level)
	return w.b
}
func AppendGzipBytesLevel(dst, src []byte, level int) []byte {
	w := &byteSliceWriter{dst}
	WriteGzipLevel(w, src, level)
	return w.b
}
// AppendGzipBytesLevel appends gzipped src to dst using the given
// compression level and returns the resulting dst.
//
// Supported compression levels are:
//
//    * CompressNoCompression
//    * CompressBestSpeed
//    * CompressBestCompression
//    * CompressDefaultCompression
//    * CompressHuffmanOnly