Update to liblzma and make kmer-counters the defaults

[lrobidou]

Hello,

The xz2 crate is unmaintained. I propose replacing it with https://github.com/portable-network-archive/liblzma-rs .

I also propose making the kmer-counters feature part of the default.

Don't hesitate to ask for 2 separate PR if needed.

Best,
Lucas.

[lrobidou]

This would solve #67 .

[Guilucand]

Hi @lrobidou, thanks for the pull request! I integrated the liblzma library change in the main branch.
For the kmer-counters default I still have to think about it if it's the best solution, as enabling it by default adds some overhead even if counters are not required.