Full refactor of the docs

[panglesd]

Big PR on the documentation side.

• It Follows the Diataxis framework,
  • Tutorials on typed presentations, drawn presentation, visual structure and custom scripts
  • Reference on syntax, special elements, actions, frontmatter, custom scripts, ...
  • A handful of how tos (including how to reveal your figure bit by bit and how to use slides instead of slips)
• It adds modifiable live examples in the docs
• It features a set of bigger examples "kept up to date".
• It adds some smaller fixes/modifications:
  • Improve -o argument wrt directories
  • Inline SVGs instead of adding them as images, allowing the use of classes and ids in SVGs
  • Refactor the Ast type to ensure exhaustive pattern matching on new nodes
• Use .woff2 for embedded fonts