Improve compression ratio

[ErdoganSeref]

Implement range asymmetric numeral systems

Integrate new compression algorithm

Add test cases

[niklasf]

Thanks for keeping up the initiative!

Among the next steps should be checking how much we gain on average, and benchmarking the throughput of compression/decompression.

Then, I guess we should check if any other smaller tweaks could be made, before preparing a migration.

[ErdoganSeref]

See #13