Merge branch 'andre-em' into 'master'

.gitlab-ci.yml

CMakeLists.txt

Data

Documentation/Examples/boundary_example.cc

Documentation/Examples/cascade_example.cc

Documentation/Examples/cascade_proton_example.cc

Documentation/Examples/em_shower.cc

Documentation/Examples/hybrid_MC.cc

Documentation/Examples/vertical_EAS.cc

Environment/BaseExponential.h

Environment/CMakeLists.txt

Environment/DensityFunction.h

Environment/Environment.h

Environment/FlatExponential.h

Environment/HomogeneousMedium.h

Environment/IEmpty.hpp

Environment/IMediumModel.h

Environment/InhomogeneousMedium.h

Environment/LinearApproximationIntegrator.h

Environment/MediumTypes.h