ftlint with MD5, acutance, and errors

[Alexei Podtelezhnikov]

Hi all,

The initial MD5 commits from Sarthak and Anurag nudged me to make a
few more changes to ftlint. It has now become a very powerful tool for
FreeType testing that:
1) verbally reports loading and rendering errors;
2) calculates horizontal and vertical acutances for quality assessment;
3) and computes MD5 to detect even small bit changes in the output.

The horizontal and vertical acutances measure how sharply the coverage
changes at the glyph edges. For monochrome bitmaps, it is always 2.0
in either X or Y direction. For antialiased bitmaps, it depends on
hinting and shape of a glyph and might approach or even reach 2.0 for
I, L, +, -, =, while it might be lower for O, S, or W. Anyhow, it is a
good hinting quality metric.

Please test ftlint with your favorite broken or working fonts and give
some feedback. I hope one day it will become a workhorse for
regression testing.

Thanks,
Alexei