Use spaces to indent style.scss

My .editorconfig file specifies that spaces are being used, so adjust
the style.scss file to match that.
Add "Fork me on GitHub" ribbon

Add a ribbon pointing to the GitHub repo using CSS generated with
http://codepo8.github.com/css-fork-on-github-ribbon/
Convert CSS for "Fork me" ribbon to SCSS

The initial CSS source for the "Fork me" ribbon had a lot of redundancy,
reduce that by converting it to use SCSS enhancements.