Changelog: Listening Page

There's now a Listening page: a feed of every listening-to-tagged post, showing the track title, artists, my commentery, and a link to play it.

Like the Photos page, the feed is assembled entirely from existing template builtins — setlist to gather the tagged posts and foreach to render each row — reading from a music frontmatter:

---
...
music:
  artist: [Ninajirachi]
  title: I Love My Computer
  kind: album
  source: bandcamp
  url: https://ninajirachi.bandcamp.com/album/i-love-my-computer
  commentary: |-
    A love letter to computers and video game sounds in the best way.
---