Extract the title from h1

[moonglum]

Currently, the title (used for the navigation) is extracted from the meta information in each of the files. Not providing a title will result in an error (for that matter, not providing meta information results in an error - that is quite hard to read). @joyheron suggested, to extract the title from the h1 tag of the page.

This way, you can use a regular Markdown file, which is probably easier for people new to aiur - and you can use files like the README.md of your project.

We would document this as the main way to provide a title. We would still keep the title meta option for two reasons:

1. backwards compatibility
2. for people that want to use a different h1 and title

Implementation notes

• The h1 would be extracted using commonmark. We already use it to render the documents, and hook into it for our handling of snippets

[FND]

As discussed elsewhere, it might be worth making a strict distinction between naked Markdown files (no front matter) and RFC 822-structured files - only the former would use h1 as title, and that's the only metadata they'll have.