* I replaced the `:external:` syntax by a cleaner one, as suggested by
@maiska.
* An implicit external reference is now impossible.
* Fix duplicate labels warnings
* Minor typos, including the word "orthographicallly" :)
This is plain rename without changing content, to help git track files
history.
Do not touch files that are going to be removed during conversion.
Thanks @parulin for the idea!