GitHub-style links to section headers on policy page (openaustralia/publicwhip#860)

Mousing-over the section heading and clicking the link icon that appears...
![image](https://cloud.githubusercontent.com/assets/103446/5422408/ded52caa-82ca-11e4-9b39-6341b39f43ba.png)

... updates the URL fragment:
![image](https://cloud.githubusercontent.com/assets/103446/5422414/2cc8511c-82cb-11e4-845a-8396c9ae1c5f.png)

I'm not sure if it's going to be obvious how this works for people that don't use GitHub. Maybe showing the link in a popover will be more usable, but I thought I'd try for a simpler solution first.