Brackets [] in link text are incorrectly escaped when roundtripped through MDAST pipeline

[huumn]

recreate:

1. in markdown: [[Documentary] The Bitcoiner: is now a slave.](https://stacker.news/items/1454433)
2. switch to compose
3. switch to markdown
4. switch back to compose

I suspect there's a precedence issue with autolink/internal links, but not for certain.

[huumn]

Happy to submit a PR if this approach works for you.

No thanks we can have one of our bots do this kind of thing.