Parallelize gzip decompression

[nh13]

Related to #13.

Impossible you say? See: http://www.hicomb.org/papers/HICOMB2019-07.pdf

[sstadick]

https://twitter.com/ducktapeprogra1/status/1443723380436385792

There are some serious limitations with the reference implementation of that, but true, it's possible! PRs accepted :)