feat(howamidoing): add custom display fn

[chrononyan]

Allows config.js to optionally override the displayed name or score of an assignment, or add some description text. Feels a bit hacky, suggestions welcome.

Sample:

Topic("Homework", [
  Assignment(`Homework 1`, 2, (props) => ({ name: `${props.name} (dropped)` })),
  ...range(2, 11).map((i) => Assignment(`Homework ${i}`, 2)),
], Infinity, null, () => ({ description: `Remaining slip days: 1` }))

[pusherbot]

All PR builds shut down.