- `render_ticket_action_control` returns now a `(label, control, hint)` tuple.
The `hint` will be used to inform the user about what will happen if the action is performed.
- `get_ticket_changes` now returns simply the dictionary containing the ticket changes, instead of that dictionary plus a description of the change. That description was barely used (only by one sample plugin), and if there's a need to warn the user, the standard `req.warning` mechanism will achieve the same effect.
Also:
- further improvements to the documentation
- adapt the sample plugins to the above API changes (well, for those not already anticipating it!)
- the !CodeReview sample plugin has also been refactored a bit
