links to sections on github with emoji in the heading are broken

[chriseppstein]

# ⭐️ My Fancy 💅 Heading is assigned an anchor id of -my-fancy--heading but markdown-toc generates an id containing character escapes instead.

[doowb]

@chriseppstein if you're using markdown-toc through the api, you can pass an optional slugify function on options. This one works for this case, but I'm not sure if it'll work for other cases:

const slugify = (title) => {
  return [...toc.slugify(title)]
    .reduce((acc, ch) => {
      if (ch.charCodeAt(0) > 255) {
        return acc;
      }
      return acc + ch;
    }, '');
};

Since we're already doing replaceDiacritics, I wonder if we could do replaceUnicode (I think that's what would it would be called).

[PixievoltNo1]

This also affect READMEs as displayed on npmjs.com - they follow the GitHub convention of stripping emoji from IDs.