Deflate

* Build fixes for certain platforms and compilers.

* libdeflate now produces the same output on all CPU architectures.

* Improved documentation for building libdeflate on Windows.

* Fixed a very rare bug that caused data to be compressed incorrectly. The bug
affected compression levels 7 and below since libdeflate v0.2. Although there
have been no user reports of the bug, and I believe it would have been highly
unlikely to encounter on realistic data, it could occur on data specially
crafted to reproduce it.

* Fixed a compilation error when building with clang 3.7.

* Various improvements to the gzip program's behavior.

* Faster CRC-32 on AVX-capable processors.

* Other minor changes.

* The CRC-32 checksum algorithm has been optimized with carryless multiplication
instructions for `x86_64` (PCLMUL). This speeds up gzip compression and
decompression.

* Build fixes for certain platforms and compilers.

* Added more test programs and scripts.

* libdeflate is now entirely MIT-licensed.

* The Adler-32 checksum algorithm has been optimized with vector instructions
for `x86_64` (SSE2 and AVX2) and ARM (NEON). This speeds up zlib compression
and decompression.

* To avoid naming collisions, functions and definitions in libdeflate's API have
been renamed to be prefixed with `libdeflate_` or `LIBDEFLATE_`. Programs
using the old API will need to be updated.

* Various bug fixes and other improvements.

* Some bug fixes and other minor changes.