code: func NewCRLChecker(cn string, shardCount int, cacheDuration time.Duration) *CRLChecker {
  	return &CRLChecker{
  		cn:            cn,
  		shardCount:    shardCount,
  		shards:        make([]lazyslot.Slot, shardCount),
  		cacheDuration: cacheDuration,
  	}
  }
docs: // NewCRLChecker initializes new CRLChecker that knows how to examine CRL of
  // a CA (identifies by its Common Name).
  //
  // It must know number of shards in advance. Usually is it just CRLShardCount.
  //
  // It will cache shards in local memory, refetching them if necessary after
  // 'cacheDuration' interval.