- moving back to original flat addressing in iterators means there is no
performance issue with using lazy evaluation
- set() method now has ~0 for a default value.
We can thus simply write 'set(i) to trun on all of the bits.
This means we can use it just like labelHashSet::set(i)
- added flip() method for inverting bits. I don't know where we might need
it, but the STL has it so we might as well too.
1f6733d91d