version 1.1.5:
- Adapt the code to the change in R 4.0.0 where matrix objects now also inherit from class "array". 

version 1.1.4:
- New LICENCE;
- Add more validation filters in order to avoid errors generated by 
inappropriate input.


version 1.1.0:
- Update following the JOSS reviewing process here
<https://github.com/openjournals/joss-reviews/issues/936>
and here <https://github.com/openjournals/joss-reviews/issues/937>;
- Fix the 3D plot for "ungrouped" mortality surface;
- Add the CITATION file.

version 1.0.0:
- First stable version on CRAN
