WIP: Adapt imports to new submodule structure

src/caoscrawler/__init__.py

src/caoscrawler/conv_impl/__init__.py

src/caoscrawler/converters/__init__.py

src/caoscrawler/converters/converters.py

src/caoscrawler/converters/hdf5_converter.py

src/caoscrawler/converters/spss.py