test with cuda advection..
Added the cuda code
Merge remote-tracking branch 'chiel/cuda' into cuda_advec
Added error handling CUDA
Pass the correct pointers (device vs host) to the GPU
Added other components to 2nd order cuda advection
Single exec() for the CUDA kernels
Bug fix in diffusion call, still wrong answers
Merge remote-tracking branch 'bart/cuda_advec' into cuda
Print errors and merged with advection