Update libzim 8.2.1 for release 0.3

[Jaifroid]

Closes #55.

[Jaifroid]

@mgautierfr At long last, I'm updating the source for the javascript-libzim build to v8.2.1 of libzim. However, in the build log, I notice a bunch of deprecation warnings related to code in the bindings, starting here. Is this something I should be worried about? It looks like the bindings are depending on methods that have been marked for deprecation (I assume in libzim itself). If this is the case, then we could be looking at the build breaking once those methods disappear. Are there simple alternatives we can substitute?

[Jaifroid]

I've tested the wasm release artefact from this PR in kiwix/kiwix-js#766, and all seems to be working fine.

[Jaifroid]

Also builds correctly from source (without using libzim WASM binary, but building it from scratch) after updating zlib to v1.3.

[mgautierfr]

I notice a bunch of deprecation warnings related to code in the bindings, starting here. Is this something I should be worried about?

They are warning about libzim using cpp features which are deprecated in c++17.
Next release of libzim will have them fixed (it is already on master).
Nothing to worry about and nothing to do on your side (maybe compile in c++11)

[Jaifroid]

OK, thanks for the reassurance @mgautierfr!

[Jaifroid]

Confirmed that wasm build from source (without libzim.a) works fine too. So this is ready to merge, and I can prepare the new release.