Embed linked Gists #494
Description
If we find a Gist link in a Markdown container, replace it with an embedded version of the Gist.
i.e.
<a href="https://gist.github.com/jgierer12/06a8e3913ce4ae608c010b6f47efd257">https://gist.github.com/jgierer12/06a8e3913ce4ae608c010b6f47efd257</a>would be replaced with (the result of)
<script src="https://gist.github.com/jgierer12/06a8e3913ce4ae608c010b6f47efd257.js"></script>