Adding support for the SPI stack chips

[hargoniX]

Sadly I was only able to get the API for the user to this form

    let mut flash: Flash<W25N<_, _>, W25N<_, _>, _> = Flash::init(spi, cs).unwrap();

If rust would not explicitly require me to place the two type parameters for the W25N it obviously knows already there it would look a lot more beautiful but for some reason it does that