GeezerVison

Checklist

• make -j4 test (UNIX)
• commit message follows commit guidelines

Affected core subsystem(s)

tools

Description of Change

This modifies the script that generates the docs to create a static link from each Stability Index callout bar to the Stability Index explanations in documentation.html. This was a first-commit request from @Trott. Here is what he pitched to me:

Many APIs have a Stability Index associated with them. Check out https://nodejs.org/dist/latest-v7.x/docs/api/modules.html#modules_modules for an example (the Modules API is Locked, Stability Index 3).
It would be great if there could be a link in the Stability Index banner to the definition of the various Stability Indexes. If I don't know what "Locked" means, then I can click the link and find out.
Modify html.js to include such a link. This will involve some HTML of course, and probably some CSS and maybe some back-and-forth about usability/styling once the PR is open.

I looked for any precedent for styling, and the best I could find is that when features are deprecated, a simple link is put to the new API to use, inside the banner. This similarly just links the first part (e.g. Stability: 2) to the documentation.html page. I'm obviously open to other styling suggestions, but this seemed the most straightforward. There doesn't seem to be any precedent in the docs for other things like a ? icon or similar.

Also I'm just linking to the main anchor for the Stability Index explanations, rather than to a specific one. My thinking here is that there are only a handful of them, and they should all fit nicely above the fold for anyone reading that page. It didn't seem necessary to create additional anchors.

Note that I had to make a couple more variables in the commit here to make the tests pass with the 80 character line limit.