Code review comment for ~cjwatson/launchpad:doc-vanilla

I've made the following changes in response to your review:

 * documented and partially scripted the process for rebuilding CSS
 * swapped Overview and Contents
 * bumped font weights back to browser defaults (I couldn't personally perceive a difference, but maybe you can)
 * improved the table of contents sidebars (though I went for consolidating onto the left sidebar rather than the right, since that seems more consistent with other sites)

We can make some changes, but I think the overall look and feel is supposed to be relatively consistent across Canonical's documentation sets, and I can see the value in that. As such, I declined to change the search bar, though I also think it's rather large, and I declined to put the Diataxis sections in the top menu since that doesn't seem to be the practice elsewhere.

Regarding the "Show source" link, I think it would be possible to change this to point directly to Launchpad, but I couldn't figure out how to do this in a reasonable amount of my time, so I deferred that. The tail of the URL does at least serve the purpose of showing where the source file lives in the tree, and I've quite often found "show source" links on other sites useful when trying to figure out how to produce some particular effect using Sphinx, so by Kant's categorical imperative I prefer to keep it for now.

Please re-review?