adds release notes to doc/changelog.md (see below) and
if this is not a patch release, updates _PKG_VERSION_{MAJOR,MINOR} and _LIB_VERSIONS_* in configure.ac
After the PR is merged,
if this is not a patch release, create a release branch with name MAJOR.MINOR.
Make sure that the branch contains the right commits.
Create commit on the release branch that sets _PKG_VERSION_IS_RELEASE in configure.ac to true.
if this is a patch release, open a pull request with the bugfixes to the MAJOR.MINOR branch.
Also include the release note commit bump _PKG_VERSION_PATCH and _LIB_VERSIONS_* in configure.ac.
Tag the commit with git tag -s vMAJOR.MINOR.PATCH.
Push branch and tag with git push origin --tags.
Create a new GitHub release with a link to the corresponding entry in doc/changelog.md.