Support ZSTD compression in-process

[johnkerl]

Issue #1342

$ ls -l x.csv*
-rw-r--r--@ 1 kerl  staff  18 Aug 19 14:44 x.csv
-rw-r--r--@ 1 kerl  staff  31 Aug 19 14:44 x.csv.zst

$ file x.csv*
x.csv:     CSV text
x.csv.zst: Zstandard compressed data (v0.8+), Dictionary ID: None

$ zstdcat x.csv.zst
a,b,c
1,2,3
4,5,6

$ mlr --csv cat x.csv
a,b,c
1,2,3
4,5,6

$ mlr --prepipe zstdcat --csv cat x.csv.zst
a,b,c
1,2,3
4,5,6

$ mlr --zstdin --csv cat x.csv.zst
a,b,c
1,2,3
4,5,6