feat: Implement TeX/PDF rendering

[jcreedcmu]

Implement the stubbed TeX endpoints for the custom blocks and inlines defined in TPiL. This enables building a .pdf of the book.

Incidentally also:

• bump the verso version up to the point that we have TeX rendering for Manual genre blocks and inlines.
• make the netlify and github pages deploys conditional on actual pushes to master in actions, so that PRs can pass CI checks.