Added vashishta GPU package for NVidia

lib/gpu/Nvidia.makefile

lib/gpu/lal_vashishta.cpp

lib/gpu/lal_vashishta.cu

lib/gpu/lal_vashishta.h

lib/gpu/lal_vashishta_ext.cpp

src/GPU/Install.sh

src/GPU/pair_vashishta_gpu.cpp

src/GPU/pair_vashishta_gpu.h