For boop.mp3, this commit adds both ID3v1 and ID3v2 tags.  For boop.ogg,
we use Vorbis metadata.

In the case of boop.mp3, this also adds a cover image. Interestingly, it
didn't seem to affect the size of boop.mp3 much, despite being ~8k.
boop.ogg seemed to be much more affected and so no cover image was added
to that version.