Add an em dash wrapper function

[h3h]

No description provided.

[avdgaag]

Thanks for this PR! I’m not sure about this change; Smartypants will already replace --- with — for you. If I’m writing an actual — myself, I wouldn’t want a script to replace it with an HTML entity—I’d rather leave the —.

Then again, there is an HTML entities function in there so this might be considered part of that (although I’d rather remove it), but then I wouldn’t expect a wrapping span tag around the —.

[h3h]

🤷‍♂️ The span wrapping is to accomplish a proper typographic hair spacing around the em dash. I don't much care about the entity-vs-character aspect. I'd agree that the — character is just fine on its own.

[avdgaag]

If it’s about achieving the proper spacing, shouldn’t we replace the span tag with hair spaces, so that it outputs  —  (or  —  for that matter)?

[h3h]

Maybe, though the span gives the author control over the spacing via their stylesheet, as different fonts may render hair spaces in non-ideal proportions. (And also allows for authors to omit the spaces entirely if they wish.)