Styleguide: update by pull request, not retro

Inspired by Thoughtbot's https://github.com/thoughtbot/guides/tree/master/code-review.
Styleguide: tweak emoji explanation
How to change this styleguide: more details

Based on reading the blog post (http://blog.crisp.se/2014/03/27/peterantman/crisp-consensus-model-2-1) more carefully.
Merge pull request #2 from henrik/styleguide-by-pullreq

Change styleguide by pull request instead