Update to 2.53, redesign the build system.

[ezdiy]

The way this is currently used is a lovecraftian fever of unmaintainable nightmare. Let's try to tackle this cthulthu:

• k2pdfopt is left in pristine for as much as possible, so that we get drag&drop code updates for future versions. For now the small patches for android etc will be done by koreader-base, but it may devolve into a tracking fork again if our changes to k2pdfopt will ever become actually invasive.
• Keep our makefile strictly utilitarian to just build the library and nothing else
• mupdf, tess and leptonica are now built in base, we get em via CFLAGS/LDFLAGS.
• patches to mupdf, tess and leptonica are explicitly pre-built via heuristic in make_patches.sh. Those are then applied during build in Bump mupdf, kopt, lept and tess koreader-base#1203 this may seem needlessly complicated, but it helps to keep things transparent what those patches are actually about compared to that horrible file-replacement thing. It also scales to bumping versions of those libraries (to an extent).

todo: Darwin build.

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This change is 

[Frenzie]

Which parts of the diff/result should I look at? Basically just the Makefile?

[ezdiy]

Ye, i should probably split it into one doing the flat replace and second with my changes to port to new APIs.

[Frenzie]

All looks like good concepts to me. 👍

[NiLuJe]

What he said ;).

(I've just realized that I wasn't watching this repo ^^).

[ezdiy]

Hmm, people are looking, better squash the bloat inbetween so they don't judge :>

[Frenzie]

Superseded by #49. Thanks for all the effort @ezdiy :-)