prepare for next release 4.3.27

Merge pull request #502 from CopernicaMarketingSoftware/connection-bl…

…ocked-notification

Implement connection.blocked notification handling

better comment

Merge pull request #497 from CopernicaMarketingSoftware/better-connec…

…tion-info

Add more information to the ConnectionStartFrame

support removal of properties from a message header

added more constructors to AMQP::Envelope

AMQP::Tagger now takes a std::string_view

Update docs to mention C++17

fix #489, Address::operator== is broken

"make install" now creates symlinks for the *.so files that no longer…

… target an absolute path