Make -v count once and accept -vv for debug output (closes #125)

urfave/cli before v2.25.5 counted a flag given by its alias twice, so
one -v or --verbose already gave debug output. Bump it to v2.27.7, the
latest v2 release, which counts it once: one -v gives verbose output,
two give debug.

Turn on urfave/cli's UseShortOptionHandling so single-letter flags
combine at the root and in every subcommand; -vv now works as the -v
help text says.

-v and --verbose together stay refused: urfave/cli v2 refuses any flag
given under two of its names.

The bump drops "[arguments...]" from usage lines, so generate and fetch
now name their arguments. Test runs now start at the default log level.

Model: opus-5-5

internal/cli/mfer.go

@@ -17,6 +17,7 @@ import (
 const (
 	cmdGenerate = "generate"
 	cmdCheck    = "check"
+	cmdFreshen  = "freshen"
 	cmdExport   = "export"
 	cmdFetch    = "fetch"
 	cmdVersion  = "version"
@@ -131,9 +132,10 @@ func commonFlags() []cli.Flag {
 
 func (mfa *CLIApp) generateCommand() *cli.Command {
 	return &cli.Command{
-		Name:    cmdGenerate,
-		Aliases: []string{"gen"},
-		Usage:   "Generate manifest file",
+		Name:      cmdGenerate,
+		Aliases:   []string{"gen"},
+		Usage:     "Generate manifest file",
+		ArgsUsage: "[path ...]",
 		Action: func(c *cli.Context) error {
 			mfa.setVerbosity(c)
 			mfa.printBanner()
@@ -227,7 +229,7 @@ func (mfa *CLIApp) checkCommand() *cli.Command {
 
 func (mfa *CLIApp) freshenCommand() *cli.Command {
 	return &cli.Command{
-		Name:      "freshen",
+		Name:      cmdFreshen,
 		Usage:     "Update manifest with changed, new, and removed files",
 		ArgsUsage: manifestArgsUsage,
 		Action: func(c *cli.Context) error {
@@ -324,8 +326,9 @@ func (mfa *CLIApp) listCommand() *cli.Command {
 
 func (mfa *CLIApp) fetchCommand() *cli.Command {
 	return &cli.Command{
-		Name:  cmdFetch,
-		Usage: "fetch manifest and referenced files",
+		Name:      cmdFetch,
+		Usage:     "fetch manifest and referenced files",
+		ArgsUsage: "[URL]",
 		Action: func(c *cli.Context) error {
 			mfa.setVerbosity(c)
 			mfa.printBanner()
@@ -368,9 +371,12 @@ func (mfa *CLIApp) run(args []string) {
 		Usage:                "Manifest generator",
 		Version:              mfa.VersionString(),
 		EnableBashCompletion: true,
-		Writer:               mfa.Stdout,
-		ErrWriter:            mfa.Stderr,
-		Flags:                commonFlags(),
+		// Lets single-letter flags combine, at the root and in every
+		// subcommand: -vv is -v -v.
+		UseShortOptionHandling: true,
+		Writer:                 mfa.Stdout,
+		ErrWriter:              mfa.Stderr,
+		Flags:                  commonFlags(),
 		Action: func(c *cli.Context) error {
 			if c.Args().Len() > 0 {
 				return fmt.Errorf("%w %q", errUnknownCommand, c.Args().First())