ractool doesn't fully suport lz4 or zstd

They're partially supported, but:

- They don't support `-cchunksize`, only `-dchunksize`.
- They don't support `-resources`.

Supporting `-cchunksize` will require implementing a 'cut' package, similar to the existing `github.com/google/wuffs/lib/zlibcut`.

Supporting `-resources` will probably require the upstream LZ4 and Zstd C libraries to provide stable API for dictionaries + streaming. Issues filed as [LZ4 #791](https://github.com/lz4/lz4/issues/791) and [Zstd #1776](https://github.com/facebook/zstd/issues/1776).