Render GitHub emojis

[cfclrk]

GitHub recognizes a special syntax for some emojis. For example: :x: is rendered as ❌.

For a complete list, see the emoji cheat sheet.

Should markdown-xwidget do the same? And how does GitHub accomplish this rendering?

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EDIT: Some more info:

Ok, apparently these icons are called octicons. Hopefully this is just another javascript source to add. Perhaps its inclusion should be optional?