Merge branch 'opencl-datahandling' into 'master'

conftest.py

pystencils/backends/cbackend.py

pystencils/backends/opencl_backend.py

pystencils/boundaries/boundaryhandling.py

pystencils/datahandling/__init__.py

pystencils/datahandling/datahandling_interface.py

pystencils/datahandling/pycuda.py

pystencils/datahandling/pyopencl.py

pystencils/datahandling/serial_datahandling.py

pystencils/display_utils.py

pystencils/gpucuda/periodicity.py

pystencils/kernelcreation.py

pystencils/opencl/__init__.py

pystencils/opencl/autoinit.py

pystencils/opencl/opencljit.py

pystencils_tests/test_cudagpu.py

pystencils_tests/test_datahandling.py

pystencils_tests/test_datahandling_parallel.py

pystencils_tests/test_opencl.py

pystencils_tests/test_staggered_kernel.py