Add suggestions support

The new option `app.Suggest` enables command and flag suggestions via
the jaro-winkler distance algorithm. Flags are scoped to their
appropriate commands whereas command suggestions are scoped to the
current command level.

Signed-off-by: Sascha Grunert <sgrunert@suse.com>

command.go

@@ -116,6 +116,11 @@ func (c *Command) Run(ctx *Context) (err error) {
 		}
 		_, _ = fmt.Fprintln(context.App.Writer, "Incorrect Usage:", err.Error())
 		_, _ = fmt.Fprintln(context.App.Writer)
+		if ctx.App.Suggest {
+			if suggestion, err := ctx.App.suggestFlagFromError(err, c.Name); err == nil {
+				fmt.Fprintf(context.App.Writer, suggestion)
+			}
+		}
 		_ = ShowCommandHelp(context, c.Name)
 		return err
 	}
@@ -244,6 +249,7 @@ func (c *Command) startApp(ctx *Context) error {
 	app.ErrWriter = ctx.App.ErrWriter
 	app.ExitErrHandler = ctx.App.ExitErrHandler
 	app.UseShortOptionHandling = ctx.App.UseShortOptionHandling
+	app.Suggest = ctx.App.Suggest
 
 	app.categories = newCommandCategories()
 	for _, command := range c.Subcommands {