sql.Rows.Scan requires pointer args, not sure how to pass that from Lua world, via luar (we can deference a pointer by using '-', not sure how to instruct luar to pass something by pointer).

NewMarkovChain returns a new MarkovChain with prefixes of prefixLen words.

Shared across all workers.

MarkovChain contains a map ("chain") of prefixes to a list of suffixes.

MarkovPrefix is a Markov chain prefix of one or more words.