code: function levelThrottle(options, levelDb) {
    if (!options) throw new Error("Please supply required options.")
    options.tokensTable = LevelTable(levelDb, options)
    return Throttle(options)
  }
docs: A npm.im/tokenthrottle implementation on top of Redis
  @param  {Object} options          [REQUIRED] The same options as npm.im/tokenthrottle, plus:
  - expiry: the number of seconds to expire untouched entires (optional)
  - prefix: an optional namespace prefix for the key (optional)
  @param  {LevelDb} levelDb     A level db to use.
  @return {TokenThrottle}           A token throttle backed by Redis