Blosc

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* Add support for SHUFFLE_AVX2_ENABLED and SHUFFLE_SSE2_ENABLED
even if AVX2 or SSE2 is not available. See PR 347. Thanks to
Thomas VINCENT.

* Upgrade internal-complib zstd from 1.5.0 to 1.5.2. Thanks to
Mark Kittisopikul.

* Many small code improvements, improved consistency and typo fixes.
Thanks to Dimitri Papadopoulos Orfanos.

* New HIDE_SYMBOLS CMake option to control the symbols exposure.
Default is ON. Thanks to Mariusz Zaborski.

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* Fix pthread flag when linking on ppc64le. See 318. Thanks to Axel Huebl.

* Updates in codecs (some bring important performance improvements):
* BloscLZ updated to 2.5.1
* Zlib updated to 1.2.11
* Zstd updated to 1.5.0

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* Updated zstd codec to 1.4.8.

* Updated lz4 codec to 1.9.3.

* New instructions on how to use the libraries in python-blosc wheels
so as to compile C-Blosc applications. See:
https://github.com/Blosc/c-blosc/blob/master/COMPILING_WITH_WHEELS.rst

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* Added `<unistd.h>` in vendored zlib 1.2.8 for compatibility with Python 3.8 in recent Mac OSX. For details, see: https://github.com/Blosc/python-blosc/issues/229.

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* More saftey checks have been implemented so that potential flaws
discovered by new fuzzers in OSS-Fuzzer are fixed now. Thanks to
Nathan Moinvaziri (nmoinvaz).

* BloscLZ updated to 2.3.0. Expect better compression ratios for faster
codecs. For details, see our new blog post:
https://blosc.org/posts/beast-release/

* Fixed the `_xgetbv()` collision. Thanks to Michał Górny (mgorny).

* The chunk format has been fully described so that 3rd party software
may come with a different implementation, but still compatible with
C-Blosc chunks.

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- The length of automatic blocksizes for fast codecs (lz4, blosclz) has
been incremented quite a bit (up to 256 KB) for better compression ratios.
The performance in modern CPUs (with at least 256 KB in L2 cache) should
be better too (for older CPUs the performance should stay roughly the same).

- Continuous integration has been migrated to GitHub actions and much
more scenarios are tested (specially linking with external codecs).
Also, a new OSS-Fuzz workflow has been added for increased detection
of possible vulnerabilities. Thanks to Nathan Moinvaziri.

- For small buffers that cannot be compressed (typically < 128 bytes),
`blosc_compress()` returns now a 0 (cannot compress) instead of a negative
number (internal error). See https://github.com/Blosc/c-blosc/pull/294.
Thanks to kalvdans for providing the initial patch.

- blosclz codec updated to 2.1.0. Expect better compression ratios and
performance in a wider variety of scenarios.

- `blosc_decompress_unsafe()`, `blosc_decompress_ctx_unsafe()` and
`blosc_getitem_unsafe()` have been removed because they are dangerous
and after latest improvements, they should not be used in production.

- zstd codec updated to 1.4.5.

- Conan packaging has been deprecated (from now on, we should try
to focus on supporting wheels only).