todo:
* Probing/Conflict resolution
* uniqueness

* defend our entries on incoming goodbye

* Unicast responses/queries
* Legacy unicast

* remove expression "rrset" from source files

* add SRV and TXT records referenced from PTR records automatically to packet
* add A and AAAA records referenced from SRV records automatically to packet

* name compression

* respect escaping in name serialization

done:
* really send goodbye packets
* refresh subscribed records only
* FLX_DNS_TYPE_ANY support
* Known-Answer suppression client part
* Known-Answer suppression server part
* make flx_server_add_text() and flx_server_add_service() variadic functions