Add support bzip3 #337
Description
bzip3 is a spiritual successor to bzip2; generally features better compression ratio. It's packaged for all major Linux distributions (Debian, Void, Gentoo, Arch, Alpine, Gentoo, NixOS, etc..) so compatibility/support should be rather wide.
Two rather notable differences from other compressors are the fact that bzip3 can utilise multithreading while compressing (using a fixed amount of jobs) and doesn't support the concept of levels (a block size needs to be passed to the compressor instead).
I recommend block sizes of 8M, 16M, 32M, 64M, 128M, 256M, 511M to map to levels 1-7. As the memory usage tends to be around 6*N (where N is the block size), caution is required to not exhaust the operating system's memory (level 7 will consume around 3GB of memory per compression thread).