I was seeing duplicate endpoints appearing under each module (typically
2 of each). This turned out to be due to the `render-operation` partial
being called multiple times (once when rendering the page, and another
when rendering the left-hand-side TOC).
We now check whether the endpoint has already been added to the list
before insertion, via a "seen" map (for quick lookup).
Any endpoint in a CS API module was not getting listed. This is because they are stored in nested pages. We need to hoist them up to the outer page, such that they can be retrieved and rendered by our endpoints TOC partial.
We needed to override Docsy's default page renderers to show it. Because
the Client-Server API uses a different render chain than the other
endpoint pages, we have to override two of Docsy's pages (`content.html` and `single.html`).
In order to reduce duplication, we then put the shared content into a
`spec-content.html` partial.
