Various tidyups and support for the BV4626 I/O board

Hi,

I spoke with you a long time back (more than year I think) about supporting this little I/O board.

I've finally found some time to actually hack on it and have written a small interface driver for it. It's not feature complete and is currently output only, but I do intend to add support for reading input pins (I want to hook up a motion sensor) and the ADC (for a temperature sensor).

With the current code, I also hooked an output pin up to a small RF transmitter that allowed me to switch on/off some wireless sockets sold by Maplin. I've factored this into a helper class that should be usable by other interfaces (e.g. I know it can work on Arduino) too.

While trying to understand the code (my python isn't great), I did a few tidyups along the way that removed dead code.

I think this is OK to merge now, but if you'd rather wait until I finish the input/ADC code or have any other suggestions, that's all fine too!

Cheers!