Undocumented "global" vars

[ehrenfeu]

Lines like these ones

https://github.com/imcf/python-imcflibs/blob/ea1e903c3d696549ea84f10c7f6ad0f1a352770a/src/imcflibs/imagej/bdv.py#L453-L455

should have:

• either proper "variable docstrings" (usually preferred)
• or be explicitly excluded from the API docs by adding a """@private""" pseudo-docstring (see lines 21 to 24 in the same file)

Pinging @lguerard