Now with working directory support

A new optional argument at the end. Omit or leave as an empty string to use the game’s working directory.

Used like so:

var winDir = environment_get_variable("WINDIR");
var cmdPath = winDir + "/System32/cmd.exe";
var root = filename_drive(winDir);
execute_shell_simple(cmdPath, "/K", "open", 5, winDir);