Rewrite it in OCaml

[panglesd]

Rewrite of the engine in OCaml.

This should have almost feature parity with the javascript engine.

• Going backward is finally fixed! (see https://choum.net/panglesd/undo-monad/ for a story about that)
• Same markup language/set of attributes
• Annotations are still possible (although, this is done in svg now, which is much better for zooming)
• Table of content (although, the table of content use the heading structure instead of the subslip hierarchy. Much more useful!)
• Subslips (although, it is based on the new auto-rescalers and the slip adapts itself to the width of the container: no need to specify a scale. Also the slips don't have their own state)

Includes a prototype for mobile support.

What it breaks: "low level" html such as <slip-slip> tags.

Thanks a lot to NLNet for the support!

[panglesd]

Note that the license has been changed from MIT to GPLv3.

[panglesd]

🎉