feature request: ability to filter a tag based on a callback

[BrianHicks]

I'm writing a tool to publish HTML from Obsidian. My tool only publishes a subset of rendered pages, and I'd like to be able to remove <a> tags that link to unpublished pages. It looks like ammonia can filter attributes based on a callback (yay!) but not yet tags—that'd be really helpful for me!

[fdemmer]

I imagine such a callback would also be useful to preserve/recreate linebreaks in text for HTML structured with <br> or <p> tags.

edit: duplicate #164 ?