Strip invisible characters from anchors

[flanakin]

Proposal

When you create a header markdown header, an anchor is created for you and special characters are removed and spaces are trimmed. This works great... mostly. There are 2 issues:

1. When an emoji is used, there are sometimes invisible characters left behind.
2. When there's a space before or after the emoji, the space isn't getting trimmed.

Proposal

Remove special and invisible characters first, then trim spaces.

Example

## 🙋‍♀️ Ask a question

To the naked eye, this looks like #-ask-a-question, which is mostly fine barring the extra space. But when you see this in the browser, it's rendered as #%EF%B8%8F-ask-a-question.

This should render as #ask-a-question without the invisible characters or extra space.

[waldyrious]

Remove special and invisible characters first

I think replacing such characters with hyphens might be more predictable / less surprising. So #-ask-a-question is the result I feel would be most intuitive. (That said, I agree that removing them altogether is an improvement over the current situation.)

[wooorm]

(I don’t work at GH)

• they don’t do slugs in this project
• changing this will break existing things, I don’t think it’s likely to happen, also because they almost never change things