Things to do before making a release:

  * Update the version number and release date in configure.ac.

  * Update the OCTAVE_API_VERSION number in configure.ac.

  * Update version number and release year in CITATION.

  * Update the etc/NEWS.N.md file corresponding to the major release
    number N.  Include release date in Summary header.

  * Update the NEWS-<VERSION>.html, index.in, news.in, and download.in
    files for the web site.

  * Copy tarballs to ftp.gnu.org.

  * Post a release announcement to the help@octave.org and
    info-gnu@gnu.org lists.

  * Update https://wiki.octave.org/Release_History page.