Implement Markdown rendering

[caseyscarborough]

Emojis do not currently get rendered in the activity feed.

[mawiegand]

It would be nice if the full GitHub Markdown will be supported and not only emojis.
Links, bold & italic text, etc. See below:

[caseyscarborough]

Great point, that would definitely be the better route.

[caseyscarborough]

If anyone is willing to give this a shot, I'd be happy to accept a pull request for this feature.