Log Message:
libdeflate: update to 1.19.

## Version 1.19

* Added new functions `libdeflate_alloc_compressor_ex()` and
  `libdeflate_alloc_decompressor_ex()`.  These functions allow specifying a
  custom memory allocator on a per-compressor basis.

* libdeflate now always generates Huffman codes with at least 2 codewords.  This
  fixes a compatibility issue where Windows Explorer's ZIP unpacker could not
  decompress DEFLATE streams created by libdeflate.  libdeflate's behavior was
  allowed by the DEFLATE RFC, but not all software was okay with it.  In rare
  cases, compression ratios can be slightly reduced by this change.

* Disabled the use of some compiler intrinsics on MSVC versions where they don't
  work correctly.

* libdeflate can now compress up to the exact size of the output buffer.

* Slightly improved compression performance at levels 1-9.

* Improved the compression ratio of very short inputs.