convert atc library header files to C++ style

lib/atc/Array.h

lib/atc/Array2D.h

lib/atc/ElectronPhononExchange.cpp

lib/atc/FE_Element.cpp

lib/atc/FE_Engine.cpp

lib/atc/FE_Interpolate.cpp

lib/atc/FE_Mesh.cpp

lib/atc/FE_Mesh.h

lib/atc/Function.h

lib/atc/GMRES.h

lib/atc/KD_Tree.cpp

lib/atc/KD_Tree.h

lib/atc/KernelFunction.cpp

lib/atc/LammpsInterface.h

lib/atc/OutputManager.cpp

lib/atc/ShapeFunction.h

lib/atc/Utility.h