Vendor reveal.js 5.2.1 (from 5.1.0)

Contains the upstream 5.2.x feature set, most notably the lightbox
(data-preview-image/data-preview-video opens media full-size in an
overlay), controls: "speaker-only", search API extensions and
speaker-view fixes. The package's local additions are carried over
unchanged: IDS theme (ids.css/ids.scss), extra theme fonts,
chalkboard/customcontrols/menu plugins, and the 1280x720 default
slide size (patched in js/config.js and the dist bundles).

Also fixes a pre-existing fork bug (unrelated to the upgrade): the
slidechanged Highcharts resize hook in default.html now checks that
Highcharts exists, no longer throwing in decks without highcharter.

Docs: README (Rmd + rendered md) gained a short Lightbox section,
NEWS.md notes the library bump.

Verified: examples/ids.html and examples/simple.html re-render and run
error-free through all 13/5 slides (Reveal.VERSION = 5.2.1); lightbox
opens on click and closes with Esc in a dedicated test deck.

Change-Id: I0751129dfb0c9d20b56241377905876314a26011
diff --git a/inst/reveal.js-5.2.1/plugin/math/mathjax3.js b/inst/reveal.js-5.2.1/plugin/math/mathjax3.js
new file mode 100644
index 0000000..68572aa
--- /dev/null
+++ b/inst/reveal.js-5.2.1/plugin/math/mathjax3.js
@@ -0,0 +1,77 @@
+/**
+ * A plugin which enables rendering of math equations inside
+ * of reveal.js slides. Essentially a thin wrapper for MathJax 3
+ *
+ * @author Hakim El Hattab
+ * @author Gerhard Burger
+ */
+export const MathJax3 = () => {
+
+    // The reveal.js instance this plugin is attached to
+    let deck;
+
+    let defaultOptions = {
+        tex: {
+            inlineMath: [ [ '$', '$' ], [ '\\(', '\\)' ]  ]
+        },
+        options: {
+            skipHtmlTags: [ 'script', 'noscript', 'style', 'textarea', 'pre', 'code' ]
+        },
+        startup: {
+            ready: () => {
+                MathJax.startup.defaultReady();
+                MathJax.startup.promise.then(() => {
+                    deck.layout();
+                });
+            }
+        }
+    };
+
+    function loadScript( url, callback ) {
+
+        let script = document.createElement( 'script' );
+        script.type = "text/javascript"
+        script.id = "MathJax-script"
+        script.src = url;
+        script.async = true
+
+        // Wrapper for callback to make sure it only fires once
+        script.onload = () => {
+            if (typeof callback === 'function') {
+                callback.call();
+                callback = null;
+            }
+        };
+
+        document.head.appendChild( script );
+
+    }
+
+    return {
+        id: 'mathjax3',
+        init: function(reveal) {
+
+            deck = reveal;
+
+            let revealOptions = deck.getConfig().mathjax3 || {};
+            let options = {...defaultOptions, ...revealOptions};
+            options.tex = {...defaultOptions.tex, ...revealOptions.tex}
+            options.options = {...defaultOptions.options, ...revealOptions.options}
+            options.startup = {...defaultOptions.startup, ...revealOptions.startup}
+
+            let url = options.mathjax || 'https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js';
+            options.mathjax = null;
+
+            window.MathJax = options;
+
+            loadScript( url, function() {
+                // Reprocess equations in slides when they turn visible
+                deck.addEventListener( 'slidechanged', function( event ) {
+                    MathJax.typeset();
+                } );
+            } );
+
+        }
+    }
+
+};