Import security advisors

Imported security files as is.
clean up announcents

Creating this separage directory was a mistake. News items are now done
as jekyll posts. The one file I put here is now in _posts.
Fix filenames in _posts

The dots and dashed were swallowed when converting the post titles
to the filenames, which makes it harder to see the version numbers.
Rename the files; no file content changed.