Email links missing `mailto:` prefix in rendered HTML

[Ote-Leo]

When rendering markdown that contains email-style links, the built-in HTML renderer generates an anchor tag without the mailto: scheme.

For example, running:

echo "You can ask [John Doe](john.doe@email.com)." | cargo run -q --

produces:

<p>You can ask <a href="john.doe@email.com">John Doe</a>.</p>

The expected behavior is for the href attribute to include the mailto: prefix, so that the link is recognized as an email link.

[hellux]

I think the current behavior matches the reference implementation's behavior, I don't wish to diverge it from it. We should implement it in jotdown if the reference implementation changes first.

With the current implementation, you could e.g.

• add mailto prefix manually: [John Doe](mailto:john.doe@email.com)
• write a filter prefixes all mail-looking links by modifying the Link events from the parser.