batch.go
func (wb *WriteBatch) SetWithTTL(key, val []byte, dur time.Duration) error {
	expire := time.Now().Add(dur).Unix()
	e := &Entry{Key: key, Value: val, ExpiresAt: uint64(expire)}
	return wb.SetEntry(e)
}
func (wb *WriteBatch) SetWithTTL(key, val []byte, dur time.Duration) error {
	expire := time.Now().Add(dur).Unix()
	e := &Entry{Key: key, Value: val, ExpiresAt: uint64(expire)}
	return wb.SetEntry(e)
}
// SetWithTTL is equivalent of Txn.SetWithTTL.