Transfer from styles repo

As mentioned in https://github.com/testthedocs/vale-styles/issues/28 this issue is to transfer the `openly` style from https://github.com/testthedocs/vale-styles/tree/master/openly to this new repo, at its top level.

Ideally, we could preserve the git commit history relevant to the files, but I'm not sure how possible that is, or if it's worth it.

Next steps (issues to be created)

- [x] Create release
- [ ] Setup linting, testing etc from existing repo
- [ ] Update existing ini files and configs in other repos to use this new repo
- [ ] Create documentation and upgrade steps