resolves asciidoctor#21 load highlight.js from a CDN

HACKING.adoc

@@ -307,6 +307,7 @@ Then run:
 == Release process
 
 
+. Make sure that the highlight plugin code embed in _lib/asciidoctor-revealjs/highlightjs.rb_ is up-to-date with the version of reveal.js
 . Do we need to do anything regarding our Opal dependency and Asciidoctor.js?
   See <<node-binary-compatibility,our section on the topic>>.
 . Update dependencies and test the package in both languages

README.adoc

@@ -231,7 +231,7 @@ The executables are built using the <<Node / JavaScript Setup,Node / JavaScript>
 * Copy or clone the reveal.js presentation framework in the directory where you will build your slidedeck.
   Here we do a shallow clone of the repo:
 
-  $ git clone -b 3.9.2 --depth 1 https://github.com/hakimel/reveal.js.git
+  $ git clone -b 3.7.0 --depth 1 https://github.com/hakimel/reveal.js.git
 
 === Convert AsciiDoc into slides
 
@@ -530,9 +530,9 @@ To override that behavior use the `width` and `height` named attributes.
 
 === Syntax highlighting
 
-Reveal.js is well integrated with https://highlightjs.org/[highlight.js] for syntax highlighting.
+reveal.js is well integrated with https://highlightjs.org/[Highlight.js] for syntax highlighting.
 Asciidoctor reveal.js supports that.
-You can activate highlight.js syntax highlighting (disabled by default) by setting the `source-highlighter` document attribute as follows:
+You can activate Highlight.js syntax highlighting (disabled by default) by setting the `source-highlighter` document attribute as follows:
 
 [source, asciidoc]
 ----
@@ -541,7 +541,26 @@ You can activate highlight.js syntax highlighting (disabled by default) by setti
 :source-highlighter: highlightjs
 ----
 
-Once enabled you can write code blocks as usual:
+[NOTE]
+----
+By default, we are using a prebuilt version of Highlight.js with 34 commonly used languages hosted on https://cdnjs.com/[cdnjs].
+You can load additionnal languages using the `:highlightjs-languages:` attribute:
+
+```
+// load yaml and scilab languages
+:highlightjs-languages: yaml, scilab
+```
+
+You can also load Highlight.js from a custom base directory (or remote URL) using the `:highlightjsdir:` attribute:
+
+```
+// load from a local path
+:highlightjsdir: highlight
+// load from jsdelivr CDN
+//:highlightjsdir: https://cdn.jsdelivr.net/gh/highlightjs/[email protected]/build
+----
+
+Once enabled, you can write code blocks as usual:
 
 [source, asciidoc]
 ....
@@ -571,7 +590,8 @@ print "$0: hello world\n"
 ....
 
 [NOTE]
-Alternatively, you can use http://coderay.rubychan.de[Coderay] or http://pygments.org[Pygments] as syntax highlighters if you are using the Asciidoctor/Ruby/Bundler toolchain (not Asciidoctor.js/JavaScript/npm).
+Alternatively, you can use http://rouge.jneen.net/[Rouge], http://coderay.rubychan.de[Coderay] or http://pygments.org[Pygments] as syntax highlighters,
+if you are using the Asciidoctor/Ruby/Bundler toolchain (not Asciidoctor.js/JavaScript/npm).
 Check the `examples/` directory for examples and notes about what needs to be done for them to work.
 They are considered unsupported by the asciidoctor-reveal.js project.
 

examples/source-highlightjs-html.adoc

@@ -2,7 +2,7 @@
 // Avoiding regressions with HTML source code inside source block
 // :include: //div[@class="slides"]
 // :header_footer:
-= HTML Source Code with Highlight.JS
+= HTML Source Code with Highlight.js
 :icons: font
 :source-highlighter: highlightjs
 

examples/source-highlightjs-languages.adoc

@@ -0,0 +1,27 @@
+// .source-highlightjs-languages
+// Demonstration of source highlighting with highlight.js using additional languages
+// :include: //div[@class="slides"] | //body/script
+// :header_footer:
+= Scilab Code with Highlight.js: using additional languages
+:source-highlighter: highlight.js
+:highlightjs-languages: yaml, scilab
+
+== Use the Source
+
+[source,scilab]
+----
+function B=gauss_filter_3_3(A)
+   x=size(A,2);
+   y=size(A,1);
+   B = zeros(y, x);
+   for j = 2:y-1
+       for i= 2:x-1
+           val= 4*A(j,i)+2*(A(j,i-1)+A(j,i+1)+A(j+1,i)+A(j-1,i))+A(j+1,i+1)+A(j-1,i+1)+A(j+1,i-1)+A(j-1,i-1);
+           B(j,i) = val/16;
+       end
+   end
+endfunction
+
+A = rand(10, 10) * 256;
+B = gauss_filter_3_3(A);
+----

examples/source-highlightjs.adoc

@@ -1,8 +1,8 @@
 // .source-highlightjs
-// Demonstration of source highlighting with highlightjs
+// Demonstration of source highlighting with highlight.js
 // :include: //div[@class="slides"]
 // :header_footer:
-= Source Code with Highlight.JS
+= Source Code with Highlight.js
 :icons: font
 :source-highlighter: highlightjs