build!: Remove contrib/tools from all builds
refactor(build): Move generators from contrib/ to scripts/generators/
doc: Remove outdated claims of differences between release archives
doc: Remove outdated claims of differences between release archives
refactor(build): Move contrib/{conftest,pngminim} to scripts/pnglibconf/
fix(build): Keep pngprefix.h out of its own generation
doc: Explain why the progressive reader keeps the zstream across chunks
doc: Explain why the progressive reader keeps the zstream across chunks