Uncited Items API

[cormacrelf]

In sum:

driver.includeUncited("None"); // Default
driver.includeUncited("All");
driver.includeUncited({ Specific: ["citekeyA", "citekeyB"] });

If a reference, known to the driver, is not cited in any of the clusters in the document, it can still be included in the bibliography if it matches the filter set by includeUncited().

This has been tested especially in the context of disambiguating using those uncited items. It lacks an actual test suite to confirm that, but the matter is almost entirely whether those items participate or not.

Also:

• Actually creates "ghost cites" of uncited items for disambiguation
• Finally allocates year-suffixes in bibliography order, per the spec, which
  can be different from cited order
• Uses pristine ghost cites, even for cited items, when forming year-suffix
  groups. Because "ibid" references can match more items' DFAs than they
  should. See that "Alloc year suffixes" commit for details.
• Workaround for some mutex issues that I have now solved (subsequent PR)