aGrUM/pyAgrum >=2.0.0 : import pyAgrum becomes import pyagrum

[phwuil]

To adhere to Python's PEP8 naming conventions, we have renamed the package from pyAgrum to pyagrum. We are aware that this change may cause some inconvenience, but it is necessary to ensure consistency with Python's style guidelines and improve the overall user experience. The transition to version 2.0.0 is the right time to implement this change, as it allows us to make a clean break and set a solid foundation for future development.