Solution: add dependency and configure flag

Solution: add build-dependency and configure option

Solution: bump changelog, ABI revision, library and packaging version

Solution: bump to 4.2.2

Solution: build-depend on asciidoc and xmlto

Solution: depend on libunwind-dev | libunwind8-dev | libunwind7-dev

Solution: update NEWS, include/zmq.h and packaging

Solution: import and adapt Debian's packaging code from
https://packages.debian.org/source/unstable/zeromq3
As noted in packaging/debian/copyright, these files are licensed
under the LGPL2+ and the copyright belongs to the authors listed in
the same file.