Zeroconf

- Fixed a performance regression introduced in 0.26.0, thanks to J.
Nick Koston (this is close in spirit to an optimization made in
0.24.5 by the same author)

- Fixed a regression where service update listener wasn't called on IP
address change (it's called on SRV/A/AAAA record changes now),
thanks to Matt Saxon

Technically backwards incompatible:

- Service update hook is no longer called on service addition (service
added hook is still called), this is related to the fix above

- Eliminated 5s hangup when calling Zeroconf.close(), thanks to Erik
Montnemery

- Reverted uniqueness assertions when browsing, they caused a
regression

Backwards incompatible:

- Rationalized handling of TXT records. Non-bytes values are converted
to str and encoded to bytes using UTF-8 now, None values mean
value-less attributes. When receiving TXT records no decoding is
performed now, keys are always bytes and values are either bytes or
None in value-less attributes.

- Fixed issues with shared records being used where they shouldn't be
(TXT, SRV, A records are unique now), thanks to Matt Saxon
- Stopped unnecessarily excluding host-only interfaces from
InterfaceChoice.all as they don't forbid multicast, thanks to
Andreas Oberritter
- Fixed repr() of IPv6 DNSAddress, thanks to Aldo Hoeben
- Removed duplicate update messages sent to listeners, thanks to Matt
Saxon
- Added support for cooperating responders, thanks to Matt Saxon
- Optimized handle\_response cache check, thanks to J. Nick Koston
- Fixed memory leak in DNSCache, thanks to J. Nick Koston

- Fixed resetting TTL in DNSRecord.reset\_ttl(), thanks to Matt Saxon
- Improved various DNS class' string representations, thanks to Jay
Hogg