code refactor

related to #8 (closed):

• I kept changes per commit small, so the number of commits got kind of numerous...

src/icartt/__init__.py

-from .dataset import Dataset, StandardNormalComments, Variable, Formats, VariableType
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+from .dataset import Dataset, StandardNormalComments, Variable, Formats, VariableType
+
+# TODO: add __version__ ?
+
+# TODO: add __all__ = ("names of exported classes etc.",) ?
\ No newline at end of file