Port Expander (working module code inside - how does it look)

Well, it seems sensible - just my 2p, but:

1. Not much can be done about that I guess... Having writePort function would at least allow people to skip the individual pins if they wanted.
   
2. digitalWrite could probably be modified such that it could detect objects with a write function, and could then call it. Same with digitalRead, pinMode, etc. It would add to code size, but probably wouldn't hurt execution speed as much. It's still unlikely to help with things like software SPI and OneWire, as they use a 'fast path' for writing to pins.
   
3. I'd be happy to add this - it may not even require writing a new function.
   
4. We could have a go at changing these. I did some quick tests, and .write is actually ~5% faster and uses less code space than digitalWrite, so changing it would make sense (unless you needed to digitalWrite arrays.