sphinx url linter that verify if we can replace a https://<something> with :ref:whatever

[Carreau]

See #42 ; I think with this we may have all relevant information;
go from domain to name of package, to get the object file, and find if a resolved url can be replaced by a reference.

for example if we have:

See `ufuncs <https://numpy.org/doc/stable/reference/ufuncs.html#ufuncs>__` 

Could suggest

See :external+numpy:`ufunc`

[Carreau]

@melissawm maybe of interest.