Centralize CLI flag set setup

internal/cli/flags.go

@@ -0,0 +1,12 @@
+package cli
+
+import (
+	"flag"
+	"io"
+)
+
+func newFlagSet(name string, stderr io.Writer) *flag.FlagSet {
+	flags := flag.NewFlagSet(name, flag.ContinueOnError)
+	flags.SetOutput(stderr)
+	return flags
+}