Adds Header links

Fixes #37 

This adds header links to all blog posts and also the "5 Years of iOS" post. Changes are pushed to staging, so you can see the results of a [regular blog post](http://staging.ashfurrow.com/blog/the-state-of-photography-in-2014/#the-world-of-the-artist), as well as the [5-year post](http://staging.ashfurrow.com/blog/5-years-of-ios/#opened-xcode).

It's not quite ideal, as the `id`s in the 5-years post belong to the headers and not the divs, so any image accompanying the div is cut off:

![screen shot 2014-12-30 at 11 31 25 am](https://cloud.githubusercontent.com/assets/498212/5577696/6a744742-9017-11e4-98ce-4735e2e93221.png)

But I'm happy enough with it. 

/cc @orta