more succinct font overview

Reorganise assortment to:
- 3 lines (uppercase, lowercase, non-letters) for better discoverability;
- letters grouped together, all with case counterparts;
- repick extended latin to cover a wider range of more common glyphs;
- include more ASCII symbols for programming and internet usage;
- reduce set of mathematical additions to a good comparison of essentials;
- restrict drawing glyphs to one example per type:
  arrow, box drawing (3 styles), block shade, dingbat.