Replaced asterix import by targeted list

[RobertoRoos]

• Should merge or drop Adopted src/ layout for easier development #146 first and then rebase this PR.

This seems to already fix most of the auto-complete issues (#145 ):

However, the doc strings aren't shown yet, which would also be expected.

[bnjmnp]

I liked this and so already merged it, but I'm not completely convinced of how the ec_datatype is handled.
Up till now I could do this

    assert obj_0x1000.data_type == pysoem.ECT_UNSIGNED32

and now need to do this:

    assert obj_0x1000.data_type == pysoem.ec_datatype.ECT_UNSIGNED32

Which is okay in general, to not spoil the whole pysoem namespace, but this still misses auto-completion and I rather like to rename ec_datatype to just DataType.