Reorganised Vorbis Comment parsing into own type

- Added FileType to Metadata to distinguish between FLAC and OGG
- TODO: fix ALAC files being identified as AAC

tag/tag.go

@@ -61,6 +61,7 @@ func main() {
 
 func printMetadata(m tag.Metadata) {
 	fmt.Printf("Metadata Format: %v\n", m.Format())
+	fmt.Printf("File Type: %v\n", m.FileType())
 
 	fmt.Printf(" Title: %v\n", m.Title())
 	fmt.Printf(" Album: %v\n", m.Album())