It seems to compress a tiny bit better.

Fixes #73

Draft:

• it may be less stable than zlib (or not bug compliant with zlib which is the defacto standard).
• it's keeping the old zlib API but we may switch to a zlib-ng API if it's nicer (less memory copy)
• the regression tests find a few files are smaller and some give a different hash, I need to check if everything is clean.
• now that zlib has a CMake file it's less important to switch to zlib-ng, even though it's also building a dynamic version we don't want, it's also installing in the wrong places
• only Windows builds will benefit from the change if we stick to the zlib API as Linux/macOS have it on the system