added support for the Intel Edison

[cfreeman]

Pin outs for the Edison are based on this 'block' from sparkfun -- https://www.sparkfun.com/products/13038

[cfreeman]

The only driver that has been tested so far is i2c ( during the development of #72 ), GPIO, LED and SPI have not been tested yet.

[cfreeman]

Ran some more tests today. GPIO works in both directions and the pin mappings all work out and line up with the 'block' from Sparkfun.

    embd.InitGPIO()
    defer embd.CloseGPIO()

    p, _ := embd.NewDigitalPin(46)
    p.SetDirection(embd.In)

    for i := 0; i < 50; i++ {
        o, _ := p.Read()
        fmt.Printf("PIN: %d\n", o)
        time.Sleep(1 * time.Second)
    }

Reading from a switch/button requires 1k pullup resistor.