Update for Sphinx >= 4.0

[jxtngx]

resolves issue#92

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[jxtngx]

Steps taken:

• Removed Black version from setup.py
• updated Python versions in setup.py to include Python >=3.9
• in get_signatures.py
  • changed from sphinx.util.inspect import Signature to from sphinx.util.inspect import signature
  • added from sphinx.util.inspect import stringify_signature
  • changed get_signature_end as shown below

def get_signature_end(function):
    sig = signature(function)
    signature_end = stringify_signature(sig, show_annotation=False)
    if utils.ismethod(function):
        signature_end = signature_end.replace("(self, ", "(")
        signature_end = signature_end.replace("(self)", "()")
    return signature_end

• ran tests (with pytest, not Docker image); results shown below

[gabrieldemarmiesse]

Sadly I don't have many right anymore in this repository. I can't approve the workflow to run. Maybe this repo could be transferred to my github username, so that I can continue to maintain it? @qlzh727 what do you think? Can we transfer this repo under @gabrieldemarmiesse ? Or do you want to keep it there and re-add me as maintainer?

[jxtngx]

The commit at bab0aa5 resolved the remaining failed test.