Breaking changes
* Deprecate and remove the `fin` attribute in XML parameters.
- The end date of a parameter is assumed to be the start of the next one.
- The `<END>` indicates that a parameter does not exist anymore
* Deprecate and remove the `fuzzy` attribute in XML parameters.
- By construction, the value of a parameter is always extended towards the future.
- To indicate a likely change of the legislation, a `<PLACEHOLDER>` can be added.
* Deprecate and remove `reforms.create_item`
- New items are created directly with the method `reforms.update_items`.
* Deprecate and remove `reforms.split_item_containing_instant`
- Splitting items does not make sense in the new convention. Use `reform.update_items` to update the parameters.