message: rename NewMsg to New

Should have done this when relocating this from container. Now is a good time to rename it before v0.3.x.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/hpkg/main.go

@@ -24,7 +24,7 @@ var (
 func main() {
 	log.SetPrefix("hpkg: ")
 	log.SetFlags(0)
-	msg := message.NewMsg(log.Default())
+	msg := message.New(log.Default())
 
 	if err := os.Setenv("SHELL", pathShell.String()); err != nil {
 		log.Fatalf("cannot set $SHELL: %v", err)