args_percentage
h = args_percentage(args, 'h', 1, tty->sy, tty->sy,
w = args_percentage(args, 'w', 1, tty->sx, tty->sx,
y = args_percentage(args, 'y', 0, PANE_MAXIMUM, w->sy, &cause);
x = args_percentage(args, 'x', 0, PANE_MAXIMUM, w->sx, &cause);
long long args_percentage(struct args *, u_char, long long,