Stream -> stream API for compression and decompression

[jhurliman]

I realize with the way this project is setup (a wrapper around a CLI executable) this would actually be using temporary files under the hood, but a nice wrapper for starting and ending with Buffer objects would be useful.

[albertdb]

Maybe it won't need temporary files, just playing with stdin and stdout. In fact, execFile returns a Buffer, so it should be easy.

[xamgore]

https://github.com/zwb-ict/node-zstd works with Buffers and is a Node.js C++ addon. There is also a fork cppzst with node 14 support.