Use intersphinx references

[dukecat0]

I ignored some links as I can't find the references for them.

[webknjaz]

Have you checked intersphinx-untangled for missing references?

[dukecat0]

Yes, I have checked. Actually, references used in the docs are found in intersphinx-untangled.

[webknjaz]

Yes, I have checked. Actually, references used in the docs are found in intersphinx-untangled.

I see. So if some links aren't there, it means that the linked sites got restructured. The best way to fix this is to find new/alternative locations for the content. Because currently, they point to the wrong pages. For example, there's https://setuptools.readthedocs.io/en/latest/setuptools.html#automatic-script-creation but that page doesn't have the title "Automatic Script Creation" anymore. I think we need to integrate sphinx's linkcheck to catch such broken links early.