EBNF rendering to HTML

[katef]

This is a quick attempt at rendering an EBNF dialect for sake of human consumption rather than for parsing. It's a made-up dialect, formatted for presentation in documentation, and presented as HTML. I hope it sits well alongside the SVG railroad diagrams for the same purpose.

Most of the time it looks something like this:

and in worser cases like this:

There you can see the hex encoding for non-printable things, which I picked for the railroad diagrams because I think it's slightly less confusing for single characters than using an escape character.

The excess parentheses appear there because this rendering is directly from the AST rather than a more convenient form for rewriting and optimisations. Hence #24.