Clean submodules for data handling and finite differences

__init__.py

boundaries/boundaryhandling.py

cpu/vectorization.py

datahandling/__init__.py

datahandling/parallel_datahandling.py

datahandling/serial_datahandling.py

datahandling/vtk.py

fd/__init__.py

fd/derivative.py

fd/finitedifferences.py

kernelcreation.py

test_simplification_strategy.py