Add black rectangle u+25ac

[clort81]

While not strictly a 'block drawing character', the 'black rectangle u+25ac is a nice addition to thin and thick horizontal lines.
▬ ... ─ ━  
I added to tiv.cpp
0x00fff000, 0x25ac, // Black rectangle < Clort >
0x00ffff00, 0x25ac, // Black rectangle < Clort >
0x000fff00, 0x25ac, // Black rectangle < Clort >
(the extra matches allow it to 'hit' more of those middle lines)

[stefanhaustein]

I wonder if we should auto-generate extra matches for some characters by shifting by one pixel in configurable directions...

That said, I had thin lines enabled before and they often look quite out of place, as they show more fine-grained structure that isn't available elsewhere...

[clort81]

i prefer to disable thin lines also ╷ ─ ┏ don't work well imo.

to get nice results I usually use the 'warp' tool in GIMP to shift regions so they align well.

I'd like to experiment with a random-shifter-of-source-image regions, and some Neural Network on the backend, scoring/judging how true to ground truth the result scores.