move codec-specific utilities into pkg/codecs

pkg/codecs/jpeg/jpeg.go

@@ -0,0 +1,13 @@
+// Package jpeg contains JPEG/JFIF markers.
+package jpeg
+
+// standard JPEG markers.
+const (
+	MarkerStartOfImage            = 0xD8
+	MarkerDefineQuantizationTable = 0xDB
+	MarkerDefineHuffmanTable      = 0xC4
+	MarkerDefineRestartInterval   = 0xDD
+	MarkerStartOfFrame1           = 0xC0
+	MarkerStartOfScan             = 0xDA
+	MarkerEndOfImage              = 0xD9
+)