[lua] add string.rep extern

std/lua/NativeStringTools.hx

@@ -145,6 +145,18 @@ extern class NativeStringTools {
 		function must be a Lua function without upvalues.
 	**/
 	public static function dump(d:Dynamic):Dynamic;
+
+
+    /**
+        Returns a string that is the concatenation of n copies of
+        the string s separated by the string sep. The default value
+        for sep is the empty string (that is, no separator).
+        Returns the empty string if n is not positive.  (Note that
+        it is very easy to exhaust the memory of your machine with
+        a single call to this function.)
+    **/
+    public static function rep(s:String, n : Int, ?sep : String) : String;
+
 }
 
 @:multiReturn extern class StringFind {