Merge remote-tracking branch 'upstream/develop' into develop

Core/Material/BaseMaterialImpl.h

Core/Material/MaterialFactoryFuncs.cpp

Core/Material/MaterialUtils.cpp

Core/Material/MaterialUtils.h

Core/Multilayer/MultiLayer.cpp

Core/Multilayer/MultiLayer.h

Core/Simulation/Simulation.cpp

Core/Simulation/SpecularSimulation.cpp

auto/Wrap/doxygen_core.i

auto/Wrap/libBornAgainCore.py

auto/Wrap/libBornAgainCore_wrap.cpp