openPin() architect improvement

[ixvick]

in
func openPin(p Pin, write bool) Pin {
}

It would be better not to call fmt.Printf() and os.Exit(1) inside openPin()
instead please return p, err

[ixvick]

func openPin(p Pin, write bool) (Pin, error) {
	flags := os.O_RDONLY
	if write {
		flags = os.O_RDWR
	}
	f, err := os.OpenFile(fmt.Sprintf("/sys/class/gpio/gpio%d/value", p.Number), flags, 0600)
	if err != nil {
                return p, err
	}
	p.f = f
	return p, nil
}