bug#64972: bibtex-autokey-get-year does not recognize biblatex date ranges

[Gustavo Barros]

Hi All,

I think this counts more as a feature request than a bug report.  But,
currently, `bibtex.el's `bibtex-autokey-get-year' cannot handle
`biblatex' date ranges, and it would be nice if it did.

For example, calling `M-: (bibtex-autokey-get-year)' with point inside
the entry:

    @Article{,
      author       = {Author, J.},
      title        = {Title},
      journaltitle = {Journal},
      date         = {2020-10/2020-12},
    }

Results in user-error "Year or date field ‘2020-10/2020-12’ invalid".

The "date" field, however, is valid `biblatex' syntax for a date
range, according to the section "2.3.8 Date and Time Specifications"
of `biblatex's manual.

Best regards,
Gustavo.