Currently `HiddenServiceExportCircuitID` specifies the protocol. As we move towards exporting as much stats as we can, I think it's better to create a new directive(`HiddenServiceExportStats`) for the protocol only. Also, I need some opinions on the directives. 1. Create directive per stat(`HiddenServiceExport*`), make all of them bound to the hidden service (in `hs_service_config_t`). 2. Create directive per stat, only `HiddenServiceExportStats` bounds to the hidden service and others are global (in `or_options_st`). 3. Don't create directive per stat, Only one directrive `HiddenServiceExportStats`, bound to the hidden service, exports all.