Make kong.Parse() global more useful.

global.go

@@ -4,13 +4,38 @@ import (
 	"os"
 )
 
+// App is the default global instance. It is populated by Parse().
+var App *Kong
+
 // Parse constructs a new parser and parses the default command-line.
 func Parse(cli interface{}, options ...Option) string {
 	parser, err := New(cli, options...)
 	if err != nil {
 		panic(err)
 	}
+	App = parser
 	cmd, err := parser.Parse(os.Args[1:])
 	parser.FatalIfErrorf(err)
 	return cmd
 }
+
+func FatalIfErrorf(err error, args ...interface{}) {
+	if App == nil {
+		panic("call kong.Parse() before using kong.FatalIfErrorf()")
+	}
+	App.FatalIfErrorf(err, args...)
+}
+
+func Errorf(format string, args ...interface{}) {
+	if App == nil {
+		panic("call kong.Parse() before using kong.Errorf()")
+	}
+	App.Errorf(format, args...)
+}
+
+func Printf(format string, args ...interface{}) {
+	if App == nil {
+		panic("call kong.Parse() before using kong.Printf()")
+	}
+	App.Printf(format, args...)
+}