Markdown-style image hotlinks no longer work

[dreeves]

### Desiderata
- [x] Manually do the workaround for all existing instances
- [x] Demote this as a regression
- [x] Narthur tries replicata
- [ ] Decide if we want to support them going forward

Replicata

1. Go to https://blog.beeminder.com/commitwall
2. Look at the screenshot in the Announcement section

Expectata

To see a screenshot.

Resultata

This mess:

Nota Nebulosa

I changed it to html (<img src="http..."/>) instead of the markdown (![image|436x301](http...)) as a workaround. I think it's rare that we used the latter format in posts but need to check.

Verbata: markdown specification of inline images, mendoza, GFM, GitHub-Flavored Markdown,

[dreeves]

Interestingly, I found this version which does work:

![image](https://user-images.githubusercontent.com/1292086/70180858-df72e600-16f1-11ea-8876-585b547e3e6c.png)

[dreeves]

I've now done the workaround for existing images. I think it would be nice to support this, since GitHub and expost both do. Eg http://doc.bmndr.co/shapeup. Unclear if it counts as a regression now since we've successfully worked around it!

[narthur]

@dreeves is the issue the image size specifically? e.g. |200x300?

[dreeves]

Seems like it! To clarify, both GitHub and Expost (the doc.bmndr.co URLs) support things like ![image|690x254](http://example.com/foo.png) but the blog doesn't.

[narthur]

Interesting. Marked is supposed to support GitHub-flavored markdown. I just checked the GFM spec and it doesn't seem to say anything about this feature. 🤔

https://github.github.com/gfm/#images

[narthur]

Testing:

![alt|50x50](https://blog.beeminder.com/wp-content/uploads/2023/05/mathboardwithbee.png)

[narthur]

@dreeves It appears that GFM doesn't break, but it also doesn't respect the size. It just treats it like part of the alt text. So I'm surprised that the cases you found did seem to break.