Make release tag an annotated tag

It is customary to use annotated tags for releases, to preserve the
information about when the tag itself was created, by whom and for what
purpose.  In our case we always have a commit directly before the tag, but
some workflows may expect annotated tags nonetheless, “git describe” among
them.  We might want to sign them one day, too.

release.sh

@@ -50,7 +50,7 @@ rm -f package.json.bak
 # Make the commit and tag, and push them.
 git add package.json bower.json
 git commit -n -m "v$VERSION"
-git tag "v$VERSION"
+git tag -a "v$VERSION" -m "v$VERSION"
 git push origin "v$VERSION"
 
 # Update npm (bower and cdnjs update automatically)