Release steps:

* Review changes compared to last release.
  make review-diff

* Make sure LT_* variables in configure.ac are updated properly.

* Make sure NEWS file contains a good summary of changes.

* Optionally check that everything builds.
  make release-check

* Replace 'unreleased' with 'released YYYY-MM-DD' in NEWS and commit
  it with a commit log like 'Version 2.13.'.

* Build tarball and update webpages.
  make release

* Email announcement, based on announce.txt.

* Create a Savannah news blurb about the release:
  https://savannah.gnu.org/news/?group=libtasn1

* Notify freecode.org.

Post-release:

* Update NEWS file for another release.