Add println function

examples/greeter.sb

@@ -4,4 +4,4 @@ fn main() {
 
 fn greet(name) {
     return "Hello " + name
-}
+}

lib/stdio.sb

@@ -1,3 +1,10 @@
+// Raw wrapper around _printf builtin function.
+// Writes the given content to stdout
 fn print(msg) {
-    _printf(msg + "\n")
+    _printf(msg)
+}
+
+// Like print(), but with an extra newline ('\n') character
+fn println(msg) {
+    print(msg + "\n")
 }