Add tests against reference libraries

[gendx]

To check that the implementation is correct, there should be tests against reference libraries such as https://crates.io/crates/lzma-sys, for example:

• compressing with one implementation and decompressing with the other,
• decompressing with both implementations and checking that the result (or error) is the same.

[Shnatsel]

I had the same idea. Fuzzing can be of great help for discovering actually interesting inputs. This sounds fairly trivial, I'll see if I can whip up an implementation.