Have a sub-char resolution in the progress bar

We can have a progress bar with more resolution than the current one (per char).

That would be using characters that represent "eights of a block":

```
>>> chars = (' ', '▏', '▎', '▍', '▌', '▋', '▊', '▉', '█')
>>> for c in chars:
... print(unicodedata.name(c))
...
SPACE
LEFT ONE EIGHTH BLOCK
LEFT ONE QUARTER BLOCK
LEFT THREE EIGHTHS BLOCK
LEFT HALF BLOCK
LEFT FIVE EIGHTHS BLOCK
LEFT THREE QUARTERS BLOCK
LEFT SEVEN EIGHTHS BLOCK
FULL BLOCK
```