* Refactoring the core ``Calendar`` classes / mixins for better understanding. Only one ``Calendar`` subclass should be imported / used in calendar classes, the rest (when possible) should be ``Mixins`` (related to #511).
* Fixed Belarus holidays related to the Orthodox calendar
* Fixed Algeria week-end days
Markdown file generated using the following command:
```
pandoc -f rst -t markdown_github --atx-headers CONTRIBUTING.rst > contributing.md
```
It's been then refined to fit the GFM format
closes #368
Bruno Bord