Merge branch 'refactor_packaging' into 'master'

src/pystencils/datahandling/parallel_datahandling.py

src/pystencils/datahandling/serial_datahandling.py

src/pystencils/datahandling/vtk.py

src/pystencils/display_utils.py

src/pystencils/enums.py

src/pystencils/fast_approximation.py

src/pystencils/fd/__init__.py

src/pystencils/fd/derivation.py

src/pystencils/fd/derivative.py

src/pystencils/fd/finitedifferences.py

src/pystencils/fd/finitevolumes.py

src/pystencils/fd/spatial.py

src/pystencils/field.py

src/pystencils/functions.py

src/pystencils/gpu/__init__.py

src/pystencils/gpu/gpu_array_handler.py

src/pystencils/gpu/gpujit.py

src/pystencils/gpu/indexing.py

src/pystencils/gpu/kernelcreation.py

src/pystencils/gpu/periodicity.py