Solution: revert the revert!

Revert "Problem: regression in 4.2.3 went unnoticed, want to release 4.2.5"

This reverts commit 5f17e26f.

Solution: revert DRAFT -> STABLE API transition so that we can do a
bugfix-only 4.2.5 release.
Will be re-reverted once tagged.

Revert "Problem: ZMQ_BINDTODEVICE has met STABLE conditions"

This reverts commit 3cb79f50.

Revert "Problem: ZMQ_MSG_GSSAPI_* have met STABLE conditions"

This reverts commit 374da420.

Revert "Problem: ZMQ_MSG_T_SIZE has met STABLE conditions"

This reverts commit 6411c4a2.

Revert "Problem: docs say STABLE API still in DRAFT"

This reverts commit 9f2f30b7.

Solution: move it from DRAFT to STABLE since it's been in a public
release, committed for 6+ months and has not changed.
Given a new STABLE symbol has been added, bump minor version number.

Solution: bump to 4.2.5

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

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.