Separated mdns_core's skv-specific bits to mdns_ospf.
TODO update.
Added foreach_values to multimap.
Added foreach to dnsdb - and using it a lot (:values makes copy of a data structure, :foreach is almost optimal way to iterate).
Refactored the cache=>own propagation to use just 3 methods: propagate, stop_propagate, and expire rr.
Some refactoring of tests (now the 3 mdns topology is truly pathological all connected to all), and improvements of the proxying logic.
Moved the MUST/SHOULDs from mdns.txt to separate file, and started tracking them un mdns_core_spec.lua. Implemented two of them. Yay.
Testcase cleanup, added _one_ testcase for draft, and implemented NSEC rdata parser. Next thing to do: actually use it at some point.