Improve compression speed

Use Huffman compression in order to fasten the compression speed as described in https://golang.org/pkg/compress/flate/#NewWriter

src/compress/compress.go

@@ -9,7 +9,7 @@ import (
 // Compress returns a compressed byte slice.
 func Compress(src []byte) []byte {
 	compressedData := new(bytes.Buffer)
-	compress(src, compressedData, 9)
+	compress(src, compressedData, -2)
 	return compressedData.Bytes()
 }