Svvamp

* Fix release number.

* Fix deployment on PyPI.

* Refactor the code completely. New architecture, especially for ``Rule`` (formerly ``Election``), avoiding
diamond inheritance. Rename most classes, properties and methods.
* Cover the code with tests. Print a message when execution reaches an uncovered part of the code.
* Fix some minor bugs.
* Documentation in numpy style.
* Tutorials are now Jupyter notebooks.
* New rules: Kim-Roush and IRV-Average.

* Correct a minor bug in Plurality.IM (voters_IM is now updated).

* Rename functions and attributes with suffix _vtb to _rk.
* Allow to define a population by both utilities and rankings.
* Add shift to Euclidean box model.
* Range voting / Majority Judgment: with a discrete set of grades, send to closest authorized grades.

* 8 population models and 23 voting systems.