Rich media embeds

Write.as is about to support rich media embeds! This works on plain URLs inserted into the body of any post, to produce this:

https://twitter.com/ilikebeans/status/1350842826305794048

Rich media is only swapped in when a URL lives on its own in the post. If it's embedded in a Markdown link like this:

[Some YouTube](https://www.youtube.com/watch?v=xDNRbyPAIao&ab_channel=TheKiffness)

It will still render like this:

Some YouTube