added toUtf8()

std/hl/_std/String.hx

@@ -172,6 +172,11 @@ class String {
 			throw "Invalid unicode char " + code;
 	}
 
+	function toUtf8() : hl.types.Bytes {
+		var size = 0;
+		return bytes.utf16ToUtf8(0, size);
+	}
+
 	@:keep function __string() : hl.types.Bytes {
 		return bytes;
 	}