Add link to the source code for each page in the API (except modules)

I added the edit page to the api which takes them to the relevant code. See attached screenshot:

![2013-05-19_2016](https://f.cloud.github.com/assets/12481/524010/72fde430-c0f3-11e2-8fa7-878018c6aded.png)

I also updated the guides page to have an edit button for the base page (/guides/)

Thanks for letting me help!