Merge branch 'add_medium_type' into 'master'

.gitignore

CMakeLists.txt

Documentation/Examples/CMakeLists.txt

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/CMakeLists.txt

Environment/Environment.h

Environment/IMediumPropertyModel.h

Environment/LayeredSphericalAtmosphereBuilder.cc

Environment/LayeredSphericalAtmosphereBuilder.h

Environment/MediumProperties.h

Environment/MediumPropertyModel.h

Environment/VolumeTreeNode.h

Environment/properties8.dat

Environment/readProperties.py

Environment/testEnvironment.cc