keys_up
This function returns a list of all the keys on the keyboard that are currently up.
int[] keys_up()
Parameters:
None.
Return value:
An array with the keys that are up, or an empty array if no keys are up or if an error occurs.
Remarks:
The difference between keys_up and keys_released is that keys_released will only return a list of the keys that the user has just released, while keys_up will return a list of the keys that are currently up regardless of whether the same keys have been reported as being up in a previous call.
Example:

    // The example will constantly monitor keys that are up. If it registers three or more keys that are not up, it will exit.

    void main()
    {
    show_game_window("Keys up Test");
    int[] key_list;
    while(key_list.length()>253)
    {
    key_list=keys_up();
    wait(5);
    }
    }