Add compression mode that will compress the data very well, but at a significant performance decrease.

Mainly for offline compression, but where decompression speed should still be high.

Comparing to 'better':

```
github-june-2days-2019.json -> (discarded) 6273951764 -> 950079555 [15.14%]; 3541.4MB/s
github-june-2days-2019.json -> (discarded) 6273951764 -> 846260870 [13.49%]; 661.5MB/s

nyc-taxi-data-10M.csv -> (discarded) 3325605752 -> 960330423 [28.88%]; 3249.5MB/s
nyc-taxi-data-10M.csv -> (discarded) 3325605752 -> 794873295 [23.90%]; 437.5MB/s

10gb.tar -> (discarded) 10065157632 -> 5650133605 [56.14%]; 3137.9MB/s
10gb.tar -> (discarded) 10065157632 -> 5250102961 [52.16%]; 390.1MB/s

consensus.db.10gb -> (discarded) 10737418240 -> 4542443833 [42.30%]; 3008.2MB/s
consensus.db.10gb -> (discarded) 10737418240 -> 4272335541 [39.79%]; 248.8MB/s
```