Tried to hack around the limits of autocomplete-plus's blacklisting model by having autocomplete-bibtex unload other autocomplete providers in Markdown documents.
There's an error I haven't tracked down yet, but on top of that, I realized that I can't guarantee (and can even expect the contrary) autocomplete-bibtex to be loaded after all other providers. So it'll have to be a modification to autocomplete-plus.
Reverted back to commit 7fd1992e3449500530fb0e423b565700f4e7acb6, as the changes I had made looked like a dead end.
Only read bibtex files when possibleWords is empty.