Cleanups

- Remove dead code
- Tweak text color for higher contrast
Update What_Is_a_Font

Rebased and cherry-picked from
eb8f200f5927b7d68b1e48a8faf93214ed3890b3.
Fix various backend issues, refactor chapters 1–8
Merge pull request #38 from adrientetar/gh-pages

Cleanup, update and fix backend – refactor Chapters 1–8