Switch default compression to zstd

The 'zstd' tool will also happily decompress lz4-encoded streams, solving the backwards compatibility problem.

Fixes issue #10 (closed), replacing !27 (closed)

mentioned in merge request !27 (closed)

added 1 commit

• b78a9986 - Install zstd in CI test env

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merged

mentioned in commit 8aff8b75