Roll up bulk inserts into a transaction

[DarrenN]

SQLite is much more efficient when bulk inserts are in a transaction: https://stackoverflow.com/questions/1711631/improve-insert-per-second-performance-of-sqlite

Get up to speed on transactions: http://docs.racket-lang.org/db/query-api.html?q=Sqlite#%28def._%28%28lib._db%2Fbase..rkt%29._start-transaction%29%29