Motivation for this change

Bump to latest version. See: https://www.willus.com/k2pdfopt/k2pdfopt_version.txt

k2pdfopt is a pain to package. Instead of shipping patches for mupdf,
leptonica, and tessertact, k2pdfopt includes modified source files for these
packages. Individual files from the {mupdf,leptonica,tesseract}_mod/
directories are intended to replace the corresponding source files in the
upstream packages, for a particular version of that upstream package.

The previous packaging approach involved manually replacing these files and
producing patches which could then be applied to those packages. The benefit
of creating and applying these patches in this way is that minor updates
(esp. security fixes) might still allow these patches to apply successfully.

The current approach creates these patches using nix. This has the benefit of
easier review and should hopefully be simpler to update in the future.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.