Anchors for messages, fields, enums, services

[jacobtolar]

This adds additional anchor links in the HTML template to make sharing a link to a specific file, message, field, enum value, or service simpler.

Motivation: We have many protobufs with hundreds of fields, it would be nice to be able to link directly to a field rather than only a message.

• Makes headers links so that if you scroll through the file and find one, you can easily grab a link directly to that section
• Adds new links for fields, enum values, and services
• Could also add links to individual service endpoints if that would be useful

If it would be preferable, I'd be happy to change this to use an icon or text next to the element rather than making the headers/fields themselves links. E.g.:

• Some File Name (link)
• field_name 🔗

I also haven't added this here but could check in a simple CSS change to highlight the item you've navigated to, e.g.:

cc @pseudomuto -- I will push the remaining changes (e.g. test fixtures, generated resources, etc) once any discussion on how this should be displayed is resolved.