Updating Markdown CSS to be similar to github.com's

-  Updated Markdown CSS to be more like Github.com's markdown
    - may need a few more margin/padding changes
- Added container around header image so only clicks on image would redirect to index
    - before random clicks in whitespace on either side of logo would redirect to index

![screen shot 2014-10-01 at 4 59 55 pm](https://cloud.githubusercontent.com/assets/521270/4483061/f1fcd982-49ad-11e4-9b79-586262351ef4.png)