Use 16:9 aspect and bump reveal.js to 5.1.0

Change-Id: I6384639329daef18a40ca55cbd3c4eab0ae500e1
diff --git a/inst/reveal.js-5.1.0/css/print/pdf.scss b/inst/reveal.js-5.1.0/css/print/pdf.scss
new file mode 100644
index 0000000..0a1c2bf
--- /dev/null
+++ b/inst/reveal.js-5.1.0/css/print/pdf.scss
@@ -0,0 +1,159 @@
+/**
+ * This stylesheet is used to print reveal.js
+ * presentations to PDF.
+ *
+ * https://revealjs.com/pdf-export/
+ */
+
+html.reveal-print {
+	* {
+		-webkit-print-color-adjust: exact;
+	}
+
+	& {
+		width: 100%;
+		height: 100%;
+		overflow: visible;
+	}
+
+	body {
+		margin: 0 auto !important;
+		border: 0;
+		padding: 0;
+		float: none !important;
+		overflow: visible;
+	}
+
+	/* Remove any elements not needed in print. */
+	.nestedarrow,
+	.reveal .controls,
+	.reveal .progress,
+	.reveal .playback,
+	.reveal.overview,
+	.state-background {
+		display: none !important;
+	}
+
+	.reveal pre code {
+		overflow: hidden !important;
+	}
+
+	.reveal {
+		width: auto !important;
+		height: auto !important;
+		overflow: hidden !important;
+	}
+	.reveal .slides {
+		position: static;
+		width: 100% !important;
+		height: auto !important;
+		zoom: 1 !important;
+		pointer-events: initial;
+
+		left: auto;
+		top: auto;
+		margin: 0 !important;
+		padding: 0 !important;
+
+		overflow: visible;
+		display: block;
+
+		perspective: none;
+		perspective-origin: 50% 50%;
+	}
+
+	.reveal .slides .pdf-page {
+		position: relative;
+		overflow: hidden;
+		z-index: 1;
+
+		page-break-after: always;
+	}
+
+	.reveal .slides .pdf-page:last-of-type {
+		page-break-after: avoid;
+	}
+
+	.reveal .slides section {
+		visibility: visible !important;
+		display: block !important;
+		position: absolute !important;
+
+		margin: 0 !important;
+		padding: 0 !important;
+		box-sizing: border-box !important;
+		min-height: 1px;
+
+		opacity: 1 !important;
+
+		transform-style: flat !important;
+		transform: none !important;
+	}
+
+	.reveal section.stack {
+		position: relative !important;
+		margin: 0 !important;
+		padding: 0 !important;
+		page-break-after: avoid !important;
+		height: auto !important;
+		min-height: auto !important;
+	}
+
+	.reveal img {
+		box-shadow: none;
+	}
+
+	/* Slide backgrounds are placed inside of their slide when exporting to PDF */
+	.reveal .backgrounds {
+		display: none;
+	}
+	.reveal .slide-background {
+		display: block !important;
+		position: absolute;
+		top: 0;
+		left: 0;
+		width: 100%;
+		height: 100%;
+		z-index: auto !important;
+	}
+
+	/* Display slide speaker notes when 'showNotes' is enabled */
+	.reveal.show-notes {
+		max-width: none;
+		max-height: none;
+	}
+	.reveal .speaker-notes-pdf {
+		display: block;
+		width: 100%;
+		height: auto;
+		max-height: none;
+		top: auto;
+		right: auto;
+		bottom: auto;
+		left: auto;
+		z-index: 100;
+	}
+
+	/* Layout option which makes notes appear on a separate page */
+	.reveal .speaker-notes-pdf[data-layout="separate-page"] {
+		position: relative;
+		color: inherit;
+		background-color: transparent;
+		padding: 20px;
+		page-break-after: always;
+		border: 0;
+	}
+
+	/* Display slide numbers when 'slideNumber' is enabled */
+	.reveal .slide-number-pdf {
+		display: block;
+		position: absolute;
+		font-size: 14px;
+		visibility: visible;
+	}
+
+	/* This accessibility tool is not useful in PDF and breaks it visually */
+	.aria-status {
+		display: none;
+	}
+}