add GPU tracer

See presentation page 32-> in 
https://raw.githubusercontent.com/geodynamics/specfem3d_globe/master/utils/BOAST_framework_to_develop_the_CUDA_and_OpenCL_routines_of_SPECFEM/tutorials_BOAST_for_OpenCL_and_CUDA_programming_of_SPECFEM3D_kernels_Brice_Videau_Kevin_Pouget_Jean_Francois_Mehaut_jun2014.pdf

Main GIT repository is https://github.com/kpouget/gpuTrace