Feat. req. Add zopfli compression format

[necros2k7]

pigz -n -b 64 -k -p 31 -11 sample.file
crabz -l 9 sample.file -o sample.gz

not much but still

[sstadick]

Thanks for making an issue! There are two issues with your comparison. First crabz uses zlib-ng backend by default whereas pigz uses zlib. Second pigz uses a different algorithm when you go over compression level 9. Which crabz does not support.

[necros2k7]

So can you perhaps beat pigz in future?)

[sstadick]

True! Want to change the title of this issue to something like "Add zopfli compression format"? That is what pigz is using when -11 is specified. It trades off a lot of speed for a modest gain in compression. You could also try compressing with mgzip format and compression turned way up (11 or 12 I think). It might get close.