address docs accessibility issues

[zingale]

fix color contrast
add back link underlining

PR summary

PR motivation

PR checklist

• test suite needs to be run on this PR
• this PR will change answers in the test suite to more than roundoff level
• all newly-added functions have docstrings as per the coding conventions
• the CHANGES file has been updated, if appropriate
• if appropriate, this change is described in the docs

[zingale]

Here's a build of the docs with these changes:

[Myndex]

Underlining by default can be anti-accessible in many cases, as it can significantly interfere with readability. Underlines in blocks of body text in particular.

Underlines are far from "best practice". Like most things related to accessibility, user preference is king.

Here is a link to a draft of a white paper and related discussion we are working on:

Myndex/SAPC-APCA#65

In short, the context of where the underline is, and the white space and density of the text, all play a role here.

Cheers,

Andrew Somers
Director of Research
Inclusive Reading Technologies
https://readtech.org/ARC/