[Docutils-develop] Change "math-output" default to MathML for HTML5 writer.

[Guenter M. <mi...@us...>]

Dear Docutils developers,

since January 2023, Chrome supports MathML (again), so now MathML support
is in Firefox, Chrome, Edge, Safari, the Android HTML view, and webkit.

As the Latex2MathML converter supports more math commands, is easier to
maintain and (potentially) offers better rendering, I propose to change
the default math-output for HTML5 from "HTML" to "MathML" in Docutils 0.22
and announce this change in 0.20.

For the HTML4 writer, I propose to keep the default at "HTML math.css",
because MathML is not officially supported by its output format
XHTML 1.0 Transitional.

Günter