2.1.0 Beta1 release

2.1.0 Beta1 release

This release contains two years of development and improvements to zlib-ng,
as well as fixes and changes inherited from zlib.

The 2.1.x version series has new targeted minumum buildsystem versions, as detailed on the Wiki https://github.com/zlib-ng/zlib-ng/wiki

Buildsystem:
- Many improvements to the CMake scripts.
- Improved support for detecting memory alignment functions.
- Improved support for unaligned access by letting the compiler promote code to unaligned if supported by the CPU.
- Remove x86 cpu feature detection for TZCNT, safely fallback to BSF.
- Enable using AVX512 intrinsics with GCC <9.

Optimizations and Enhancements:
- Decompression is a lot faster (56% faster measured on AVX2-capable x86-64)
- Compresson is improved for Level 9, at the cost of a little performance.
- Compression is improved for Level 3, by switching from deflate_fast to deflate_medium.
- Levels 3 and 4 have been reconfigured to provide a better gradual tradeoff for speed/compression between levels 2 and 5.
- Deflate_quick (Level 1) has been improved to default to a bigger windowsize and support changing the window size like the other levels.

New instruction set optimizations:
- Adler32 implementation using AVX512, AVX512-VNNI, VMX.
- CRC32-B implementation using VPCLMULQDQ & IBM-Z.
- Slide hash implementation using VMX.
- Compare256 implementations using SSE2, Neon, & POWER9.
- Inflate chunk copying using SSSE3 & VSX.

Compatibility and Porting:
- CRC-32 computation changes from madler/zlib. zlib-ng/zlib-ng#a6155234
- Compatible and up-to-date with zlib 1.2.13.
- Removed the usage of macros in zlib-ng.h, making life easier for languages that want to call the C functions without having the C preprocessor (Python, etc).

Improved support more environments:
- Apple M1
- vcpkg
- Emscripten

Testing:
- Tests have been converted to use GTest. Many new tests have also been added.
- Gbench support has been added to easily benchmark changes to performance-critical functions.

Misc:
- Several pieces of core code has been restructured or rewritten.
- Too many changes to list here, see the git commit log for the full list of changes.

Deprecations:
- Configure no longer has the full range of tests.
- NMake is no longer actively supported and tested, it is now community supported.
- See the wiki for minimum build system versions and deprecations https://github.com/zlib-ng/zlib-ng/wiki