Nordic "nRF52840 Dongle" Support

It'd be great if you could - thanks! Please could you try and make it so that advertising_init and jsble_advertising_start are merged on SDK13 as well? It's nice to try and keep the ifdef nightmare as small as possible :)

For the IO, I'd check jshPinSetValue and similar stuff in jshardware.c: https://github.com/espruino/Espruino/blo­b/master/targets/nrf5x/jshardware.c#L652­

I guess there might be a different function to nrf_gpio_pin_write needed for GPIO1? If so, I'd add an 'if' based on pinInfo[pin].port and ensure that the port gets set correctly in the BOARD.py file.