This version supersedes all previous releases from the 0.21.x series, and includes
some some extra bug fixes in comparison with the previous 0.21.4 release.
This version also contains a major restructuring in the installation and
development documentation included in the source, respectively in the INSTALL
and HACKING files. We encourage everyone to give it a try and report to us any
missing information from the docs so that we can improve it even more.