Oxipng: download ældre versioner

• [Build] Fix package metadata shown in generated man page.

- [Performance] Improve Bigrams performance, giving notably faster results at lower levels.
- [Improvement] Change --np flag to also prevent conversion to indexed from other color types.
- [Improvement] Improve support for recompressing ICC profiles with high compression ratios.
- [Misc] Add warning when --ziwi exceeds --zi.
- [Build] Further reduce size of binaries.

- [Feature] Add --json option for machine-readable output.
- [Improvement] New default output with file counter and summary. (Use an extra -v flag to get the same output as before.)
- [Bugfix] Fix fast mode sometimes giving suboptimal results for small, indexed images.

- [Breaking] CLI: Change short zopfli flag from -Z to -z.
- [Breaking] CLI: Change --pretend/-P to --dry-run/-D.
- [Breaking] CLI: Change --interlace options from 1/0 to on/off.
- [Breaking] API: Change Options.interlace: Option<Interlacing> to Options.interlace：Option<bool>.
- [Breaking] API: Change Options.filter: IndexSet<RowFilter> to Options.filters：IndexSet<FilterStrategy>.
- [Breaking] API: Change Options.deflate: Deflaters to Options.deflater：Deflater.
- [Breaking] API: Change Deflaters::Zopfli { .. } to Deflater::Zopfli(ZopfliOptions { .. }).
- [Breaking] API: Change optimize() to return (usize, usize), with original and optimized sizes.
- [Feature] Allow zopfli iterations higher than 255.
- [Feature] Add --ziwi option for zopfli iterations without improvement.
- [Feature] Add --max-raw-size option to skip images that are too large.
- [Feature] Add --brute-level and --brute-lines options for advanced control of Brute filter.
- [Improvement] Reduce memory usage for fast mode.
- [Improvement] Slightly improve compression with Brute filter at levels 5 and 6.
- [Misc] Change --preserve option to no longer preserve last access time.
- [Misc] Make help output colored.

- [Feature] Add --sequential option to process files sequentially rather than in parallel.
- [Performance] Update to latest Zopfli with greatly improved performance.
- [Improvement] Reduce memory usage.
- [Bugfix] Correct handling of grayscale conversion when ICC profile is present.

- [Improvement] Improve optimization of APNG files (reductions still not supported yet).
- [Improvement] Improve reductions for small images and ensure consistent results for repeat runs.
- [Build] Add feature system-libdeflate to use the system-installed version of libdeflate.
- [Misc] Strip C2PA metadata by default.

- [Feature] Add --zi option to control the number of Zopfli iterations.
- [Improvement] Allow setting compression level to 0.
- [Performance] Improve filtering performance for some images.
- [Build] Move man page generation to an xtask.

- [Bugfix] Fix --nx still applying deinterlacing by default.
- [Bugfix] Fix wildcard matching being case-sensitive on Windows.
- [Bugfix] Fix optimized APNGs not being compatible with some programs.
- [Build] Fix feature sanity-checks not working without parallel.
- [Misc] Resolve ambiguity between optional dependencies and crate features.