Updates to conform to the new <context-free-parser> output.

@ebidel:

This mostly matches the changes to `<core-doc-viewer>` in https://github.com/Polymer/core-doc-viewer/pull/34, with some tweaks to get it to use the proper URL for element collections.

I'm using `data-anchor-id` attributes here under the assumption that's what's going to be used for deep-linking once https://github.com/Polymer/docs/pull/836 goes into effect, but if we go with a different attribute name, I can swap that out.

I left the existing styling as-is rather than copying over the styles that were added to `<core-doc-viewer>` to keep things consistent.

It looks like:
![6534933591883776](https://cloud.githubusercontent.com/assets/1749548/5462063/974b0690-853e-11e4-8fdf-bbd368c2d475.png)