Use padding between sections instead of margins

I was just introduced to kraken.js by @billwscott at JSConf today.  Looks really nice, great work!

Throwing up this PR since I noticed the left hand side menu didn't trigger quite where my eyes were reading.  So I just change the title elements' to use padding to increase their height's so they trigger the menu highlights a little earlier when scrolling.  If this somehow causes more problems than it's worth, feel free to reject :)

Before:

![image](https://cloud.githubusercontent.com/assets/49288/3109353/b96998a8-e698-11e3-8f3c-642febacab53.png)

After:

![image](https://cloud.githubusercontent.com/assets/49288/3109355/c35bf680-e698-11e3-8647-c3c1fba1f4c8.png)