Hufnagel font: glyph drawing progress

Tracking which Hufnagel glyphs are drawn so far, so anyone can spot if something's missing. Font source is on the zih-syuan/hufnagel-font branch; shapes are still being refined and this issue will get updated as drawing progresses.

**Preview**

**Drawn** (Shape still being refined)
- C clef, F clef (one F clef only, decided not to keep a second variant)
- Custos
- Punctum
- Virga
- UDV (upside-down virga)
- Liquescent up
- Clivas A for the 2nd, 3rd, 4th, and 5th interval

**Drawn as placeholder, shape still undecided**
- Liquescent down: drew a question mark until the actual shape is decided.

**As far as I know, not part of Hufnagel notation**
- G clef, diamond (inclinatum), quilisma, oriscus