Diary cleanup

This commit includes a few basic changes to make the User Diaries friendlier and easier to read. I adjusted the text styles and added a maximum width, to keep the line length under control

Here's a screenshot:

![Screen Shot 2013-03-14 at 6 18 30 PM](https://f.cloud.github.com/assets/108094/261471/3f973ba0-8cf5-11e2-9248-391c185c5d75.png)

While working on the diary, I also modernized the markdown reference sheet with better markup and clearer styles:

![Screen Shot 2013-03-14 at 6 19 49 PM](https://f.cloud.github.com/assets/108094/261475/6247838a-8cf5-11e2-8efa-a53f7acf7a9e.png)