v0.4.0

The major changes brought by this release are:

• Simplification of the interface with one method for creating the model and one method to create a background IRFs for a dataset
• Allow to have irregular energy axis for computation (interpolated to a regular one for the final model)
• Allow to have a dynamic size for the bins of the energy axis for computation
• Allow to split data in two azimuth hemisphere east/west
• Add support for gammapy 2.0
• Improvement on the logs messages
• A few bug fixes

Contributor to this release :
@gabemery
@mdebony