Update to reveal.js 4.1.2 (#136)

- New tools/ script to manually keep step for updates
- Plugins are all updated
- Template update following latest Pandoc version
- updated README for documentation
- Help page updated 
- See other change in NEWS file
diff --git a/inst/reveal.js-4.1.2/css/theme/template/mixins.scss b/inst/reveal.js-4.1.2/css/theme/template/mixins.scss
new file mode 100644
index 0000000..17a3db5
--- /dev/null
+++ b/inst/reveal.js-4.1.2/css/theme/template/mixins.scss
@@ -0,0 +1,45 @@
+@mixin vertical-gradient( $top, $bottom ) {
+	background: $top;
+	background: -moz-linear-gradient( top, $top 0%, $bottom 100% );
+	background: -webkit-gradient( linear, left top, left bottom, color-stop(0%,$top), color-stop(100%,$bottom) );
+	background: -webkit-linear-gradient( top, $top 0%, $bottom 100% );
+	background: -o-linear-gradient( top, $top 0%, $bottom 100% );
+	background: -ms-linear-gradient( top, $top 0%, $bottom 100% );
+	background: linear-gradient( top, $top 0%, $bottom 100% );
+}
+
+@mixin horizontal-gradient( $top, $bottom ) {
+	background: $top;
+	background: -moz-linear-gradient( left, $top 0%, $bottom 100% );
+	background: -webkit-gradient( linear, left top, right top, color-stop(0%,$top), color-stop(100%,$bottom) );
+	background: -webkit-linear-gradient( left, $top 0%, $bottom 100% );
+	background: -o-linear-gradient( left, $top 0%, $bottom 100% );
+	background: -ms-linear-gradient( left, $top 0%, $bottom 100% );
+	background: linear-gradient( left, $top 0%, $bottom 100% );
+}
+
+@mixin radial-gradient( $outer, $inner, $type: circle ) {
+	background: $outer;
+	background: -moz-radial-gradient( center, $type cover,  $inner 0%, $outer 100% );
+	background: -webkit-gradient( radial, center center, 0px, center center, 100%, color-stop(0%,$inner), color-stop(100%,$outer) );
+	background: -webkit-radial-gradient( center, $type cover,  $inner 0%, $outer 100% );
+	background: -o-radial-gradient( center, $type cover,  $inner 0%, $outer 100% );
+	background: -ms-radial-gradient( center, $type cover,  $inner 0%, $outer 100% );
+	background: radial-gradient( center, $type cover,  $inner 0%, $outer 100% );
+}
+
+@mixin light-bg-text-color( $color ) {
+	section.has-light-background {
+		&, h1, h2, h3, h4, h5, h6 {
+			color: $color;
+		}
+	}
+}
+
+@mixin dark-bg-text-color( $color ) {
+	section.has-dark-background {
+		&, h1, h2, h3, h4, h5, h6 {
+			color: $color;
+		}
+	}
+}
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