DOC: Rename sphinx.ext.jsmath to sphinxcontrib.jsmath

.. and add some minor doc improvements to it.

Superseeds sphinx-doc#13785.

Author: timhoffm

doc/usage/extensions/math.rst

@@ -318,14 +318,18 @@ Sphinx but is set to automatically include it from a third-party site.
       This has been renamed to :confval:`mathjax2_config`.
       :confval:`mathjax_config` is still supported for backwards compatibility.
 
-:mod:`sphinx.ext.jsmath` -- Render math via JavaScript
-------------------------------------------------------
+:mod:`sphinxcontib.jsmath` -- Render math via JavaScript
+--------------------------------------------------------
 
 .. module:: sphinx.ext.jsmath
    :synopsis: Render math using JavaScript via JSMath.
 
 This extension works just as the MathJax extension does, but uses the older
-package jsMath_.  It provides this config value:
+package jsMath_. jsMath is no longer actively developed, but it has the
+advantage that the size of the JavaScript package is much smaller than
+MathJax.
+
+Config value:
 
 .. confval:: jsmath_path
    :type: :code-py:`str`
@@ -337,7 +341,7 @@ package jsMath_.  It provides this config value:
    The path can be absolute or relative; if it is relative, it is relative to
    the ``_static`` directory of the built docs.
 
-   For example, if you put JSMath into the static path of the Sphinx docs, this
+   For example, if you put jsMath into the static path of the Sphinx docs, this
    value would be ``jsMath/easy/load.js``.  If you host more than one
    Sphinx documentation set on one server, it is advisable to install jsMath in
    a shared location.
@@ -347,5 +351,5 @@ package jsMath_.  It provides this config value:
 .. _dvisvgm: https://dvisvgm.de/
 .. _dvisvgm FAQ: https://dvisvgm.de/FAQ
 .. _MathJax: https://www.mathjax.org/
-.. _jsMath: https://www.math.union.edu/~dpvc/jsmath/
+.. _jsMath: https://www.math.union.edu/~dpvc/jsMath/
 .. _LaTeX preview package: https://www.gnu.org/software/auctex/preview-latex.html