doc work + type hints in artifacts.py [part 1] (#109)

* start doc update for n-g- funcs

* continued docs work in n-g-()

* continued artifacts.py docwork

* Update sgeop/artifacts.py

Co-authored-by: Martin Fleischmann <[email protected]>

* Update sgeop/artifacts.py

* martin comments & clarifications -- #108

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Co-authored-by: Martin Fleischmann <[email protected]>