Add configuration option for Chicago disambiguation

[bdarcus]

Per notes in #120:

year suffixes can only be used for single-author works (15.20); multi authors are disambiguated using names and'/or short titles (I didn't realize this; will need to think on how to address it)

So the Chicago disambiguation rules are awfully complex; in some cases, one disambiguates on the year, and in the others, on the author names and/or titles.

Would need an option something like this for the first part:

year-suffix:
   single-author-only # default would be all

I have no idea how to implement the second part of that, for multi-author works.

It could be would need to combine into one setting:

disambiguate:
  suffix-all # default, at least for author-date

disambiguate:
  suffix-single-author-names-rest

... or even just:

disambiguate:
  chicago-author-date

But need to dig into the exact logic for the second part; I worry different styles of this sort may have different rules, and it might get unmanageable.