Several modifications to make the code more standard conform and document it

corsika/detail/media/BaseExponential.inl

corsika/detail/media/Environment.inl

corsika/detail/media/FlatExponential.inl

corsika/detail/media/HomogeneousMedium.inl

corsika/detail/media/InhomogeneousMedium.inl

corsika/detail/media/LayeredSphericalAtmosphereBuilder.inl

corsika/detail/media/LinearApproximationIntegrator.inl

corsika/detail/media/MediumPropertyModel.inl

corsika/detail/media/NuclearComposition.inl

corsika/detail/media/ShowerAxis.inl

corsika/media/Environment.hpp

corsika/media/IMagneticFieldModel.hpp

corsika/media/MediumProperties.hpp

corsika/media/MediumPropertyModel.hpp

corsika/media/NuclearComposition.hpp

corsika/media/NuclearComposition_old.hpp

corsika/media/ShowerAxis.hpp

corsika/media/UniformMagneticField.hpp

src/media/CMakeLists.txt

src/media/readProperties.py