Summary of important user-visible changes for pkg-octave-doc 0.7.3:
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 ** Demo figures are now saved as SVG instead of PNG and drawn at a reduced
    size, for sharper and lighter documentation pages.

 ** Each demo is rendered as a collapsible "Example" card.  On classdef pages
    the cards start collapsed to keep long pages short, while function pages
    and grouped-classdef method pages keep them expanded.

 ** Examples can be cross-referenced from within a docstring: write
    `@url{#exampleN}` and it links to that demo's card on the same page,
    automatically expanding and scrolling to it when followed.  The short
    reference is expanded to a unique per-owner anchor, so references never
    collide even when several members' demos share one page.

 ** Restored math rendering by loading MathJax from a live CDN; the formerly
    used `cdn.mathjax.org` was retired in 2017, so `@tex` / `$$` display math
    had silently stopped rendering on generated pages.

 ** Updated the README documentation guidelines to cover example
    cross-references and the collapsible demo cards.

