demo: call println, c.Printf, fmt.Println

_demo/hello/hello.go

@@ -1,11 +1,15 @@
 package main
 
 import (
+	"fmt"
+
 	"github.com/goplus/llgo/c"
 )
 
 func main() {
-	c.Printf(c.Str("Hello world\n"))
+	println("hello world by println")
+	fmt.Println("hello world by fmt.Println")
+	c.Printf(c.Str("Hello world by c.Printf\n"))
 }
 
 /* Expected output: