Updated styles

I've updated the api page to match our existing styles as much as possible.
Active sidebar links are included.
![api_updated_styles](https://f.cloud.github.com/assets/101226/707588/227c849c-de23-11e2-99e2-5e309a2325fb.png)

Also, I updated the top-right header links to be active when on the specific page.
![guide_with_bolded_header_link](https://f.cloud.github.com/assets/101226/707590/4ade57d0-de23-11e2-928e-ed99c3151d76.png)