Add CHANGELOG

[dencold]

I've kept a small list of changes/enhancements over the original fork in the attribution section of the README.md file. The better way to handle this is to create a proper CHANGELOG file that keeps a chronological log of everything that has changed in the repo. Once we have a 1.0 release ready with a stable guide for others to use the theme, this will become extremely handy for users to keep track of what is going on.

A very helpful resource is this guide to maintaining changelogs:
http://keepachangelog.com/