* refactor: move tr_tracker_http_announce() helper funcs into their own namespace
* refactor: move tr_globalIPv6() helper funcs into their own namespace
* refactor: move tr_address_is_valid_for_peers() helper funcs into their own namespace
* refactor: make tr_address_compare() a private method
* refactor: rename tr_address::isIPv4() to is_ipv4()
* refactor: use snake_case for tr_address methods
* refactor: make tr_address_is_valid_for_peers() a member function
* refactor: make tr_peer_socket.type private
* refactor: reimplement tr_peerIo::address() as a wrapper around tr_peer_socket::address()
* refactor: remove tr_address, tr_port from tr_peerIo
* refactor: replace tr_netClosePeerSocket() with tr_peer_socket::close()
* refactor: add a Mediator class to decouple tr_session and tr_port_forwarding
* refactor: add tr_port_forwarding::Mediator::privatePeerPort()
* refactor: add tr_port_forwarding::Mediator::onPortForwarded()
* chore: avoid unnecessary include of timer.h in other headers
* refactor: use a uniform timerMaker() API in mediators
* chore: use typesafe sin_addr assignment instead of memcpy()
* refactor: make tr_dhtPrintableStatus private
* refactor: make tr_dhtStatus() private
* refactor: make tr_dht status enum private
* refactor: add safety mutex wrapper around libdht API calls
* refactor: make tr_dht::Status an enum class
* refactor: rename private functions
* refactor: const correctness
* refactor: use typesafe assignment instead of memcpy
* refactor: tr_session does not directly call tr_dht
* refactor: tr_dhtPort() returns std::optional
* refactor: use tr_address::fromCompact4 in tr-dht.cc
* refactor: make tr_peerIoSetEnabled() a member method
* refactor: make tr_peerIoFlushOutgoingProtocolMsgs() a member method
* refactor: make tr_peerIoFlush() a member method
* refactor: make tr_peerWriteBytes() a member method
* refactor: make tr_peerWriteBuf() a member method
* refactor: make tr_peerIoGetWriteBufferSpace() a member method
* chore: remove unused declaration
* refactor: make tr_peerIoUtpInit() a member method
* refactor: make tr_peerIoNew() a member method
* refactor: make tr_peerIoNewOutgoing() a member method
* refactor: make tr_peerIoNewIncoming() a member method
* refactor: make tr_peerIoReadBytes() a member method
* refactor: make tr_peerIoReadUint8() a member method
* refactor: make tr_peerIoReadUint16() a member method
* refactor: make tr_peerIoReadUint32() a member method
* refactor: make tr_peerIoSetIOFuncs() a member method
* refactor: make tr_peerIoReconnect() a member method
* refactor: make tr_peerIoClear() a member method
* refactor: make tr_peerIoDrain() a member method
* refactor: move evbuffer_add_hton_16() impl to cc
