Support non-alphanumeric characters in ToC (#756)

* Support non-alphanumeric characters in ToC

```js
// Note: character range in regex is roughly "word characters including accented" (eg: bublé)
const id = text
  // korean, Japanese (hiragana)
  .replace(/[^가-힣\u3041-\u3096]/g, '');
```

If want to keep existing intent, the above code might be more suitable.

But i haven't opinion yet, so I remove the one line that erased non-alphanumeric characters.

Reference issue comment: preactjs/preact-www#754 (comment)

* Filter out programming/markdown characters only

Co-authored-by: Jason Miller <[email protected]>

src/lib/content.js

@@ -158,8 +158,7 @@ function generateToc(markdown) {
 		// Note: character range in regex is roughly "word characters including accented" (eg: bublé)
 		const id = text
 			.toLowerCase()
-			.replace(/[\s-]+/g, '-')
-			.replace(/[^a-z0-9\u00C0-\u024F-]/g, '');
+			.replace(/[\s-!()<>`'"&,]+/g, '-')
 		toc.push({ text, id, level });
 	}
 	return toc;