Add support for ZSTD compression/decompression

[eroberson]

readr currently supports gz, bz2, xz, and zip. The ZSTD compression format has potentially better compression and streaming decompression performance overall than these other formats. Given the ever increasing size of datasets, the cost of storing uncompressed data, the need for performant decompression on demand, and the support readr already has for seamless reading/writing to compressed formats, it's worth exploring adding this algorithm to the package.

ZSTD description

ZSTD repo