Tune autocorrect to produce fewer false positives. Before we used
trigram similarity. Now we use Levenshtein edit distance with a dynamic
typo threshold. Trigram similarity was able to correct large
transpositions (e.g. `miku_hatsune` -> `hatsune_miku`), but it was bad
at correcting small typos. Levenshtein is good at small typos, but can't
correct large transpositions.
