Support for boost::intrusive::set

I have added visualizers for boost::intrusive::set and and associated iterator. There are four flavors:
base_hook default
member_hook default
base_hook / constant_time_size<false>
member_hook / constant_time_size<false>

I tried to add visualizers for intrusive lists with constant_time_size<false> but the visualizer code does not seem to support it.