[demand] add compression support format xz 7z zstd

[andykimpe]

please add compression support

Is it possible to add more compression support?

for xz add option

--xz: Use xz for compression.

https://github.com/tukaani-project/xz

for 7z add option

--7z: Use 7z for compression.

https://sourceforge.net/projects/p7zip/files/p7zip/

for zstd add option

--zstd: Use zstd for compression.

https://github.com/facebook/zstd

these 3 formats have much higher compression than gzip or bzip2

please see if this is feasible

[megastep]

We already have these (except for 7z I guess):

    --gzip             : Compress using gzip (default if detected)
    --pigz             : Compress with pigz
    --zstd             : Compress with zstd
    --bzip2            : Compress using bzip2 instead of gzip
    --pbzip2           : Compress using pbzip2 instead of gzip
    --bzip3            : Compress using bzip3 instead of gzip
    --xz               : Compress using xz instead of gzip
    --lzo              : Compress using lzop instead of gzip
    --lz4              : Compress using lz4 instead of gzip