Reduce redundante call to bytes.ToLower and substitute the last call by an home made version doing the conversion in place

Former-commit-id: d9ea22f649d97be352f8dbb37acc1495df830118

pkg/obiformats/genbank_read.go

@@ -69,7 +69,7 @@ func _ParseGenbankFile(source string,
 			case line == "//":
 				log.Debugln("Total lines := ", nl)
 				sequence := obiseq.NewBioSequence(id,
-					bytes.ToLower(seqBytes.Bytes()),
+					seqBytes.Bytes(),
 					defBytes.String())
 				sequence.SetSource(source)
 				state = inHeader