Integrate excerpt filter anchor links

[piperhaywood]

Dropped this b/c I was having trouble accessing the excerpt w/in a loop, turns out it is as simple as post.data.page.excerpt.

[piperhaywood]

Should link to anchor link, if possible

[piperhaywood]

This is related to #49

[piperhaywood]

I’ve now changed this to how Eleventy prefers it:

https://www.11ty.io/docs/data-frontmatter/#example%3A-parse-excerpts-from-content

I’ve updated the Mozfest post to use this, you’ll see a <!-- more --> tag where the Read more button goes. This is very similar to the way WordPress handles it.

Going to leave this open since ideally, I would like to have it link to an anchor link (again, similar to WordPress behaviour) but that can come slightly later.