Emoji. :metal:

See #815.

Only emojifying PR bodies for now. 
 
As I got into this, I realized there are a lot of copyright issues. I pulled down the entire emoji archive from [emoji-cheat-sheet](https://github.com/arvida/emoji-cheat-sheet.com) but there are several licensing issues. I'll let you decide how to proceed - none of the open source solutions I could find were very satisfactory.

Also, adding all of these images into app/assets will greatly slow down your precompile. I recommend turning on `serve_static_assets` and moving these into your public directory, along with the use of a caching CDN.