OpenSlide Java release process

[x] Run test build and make distcheck
[x] Update CHANGELOG.md and versions in configure.ac and meson.build
[x] Create and push signed tag
[x] git clean -dxf && meson setup builddir && meson dist -C builddir
[x] Attach release notes to GitHub release, set pre-release flag, and upload tarball
[x] Update openslide-winbuild
[x] Update website: _data/releases.yaml, _includes/news.md
[x] Send mail to -announce and -users

openslide / openslide-java