Hawk review concepts

* [x] Clarify usage of token versus of identifier
* [x] Review and improved doc
* [x] Reformat of current credentials in hello (?..maybe wrong to mention credentials)
* [ ] Complete glossary

For this pull request, its author has lost 12 points of energy.
Please avoid using user, we removed it, use token instead. also hawk_id is more specific because it is the derived id from the token.