Example for new highlighting features

exampleSite/content/highlightjs-linenumbers-example/_index.md

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+title = "Reveal.js 3.9.0 highlighting example"
+outputs = ["Reveal"]
+
+[reveal_hugo]
+theme = "white"
+highlight_theme = "vs"
++++
+
+## New highlighting features Presentation
+
+---
+
+This presentation shows the use of the [new highlighting features](https://github.com/hakimel/reveal.js/blob/master/README.md#step-by-step-highlights) which were introduced with Reveal.js [v3.9.0](https://github.com/hakimel/reveal.js/releases/tag/3.9.0)
+
+---
+
+## Prerequisite
+
+First, disable `CodeFences` in to your `config.toml`:
+
+{{< highlight toml "style=github" >}}
+[markup.highlight]
+codeFences = false
+{{< /highlight >}}
+
+---
+## Theme
+
+Specify a theme for Highlight.js in `config.toml`
+
+{{< highlight toml "style=github" >}}
+[params.reveal_hugo]
+highlight_theme = "github"
+{{< /highlight >}}
+
+or in the `frontmatter`
+
+{{< highlight toml "style=github" >}}
+[reveal_hugo]
+highlight_theme = "github"
+{{< /highlight >}}
+
+---
+
+## Usage
+
+The line highlighting is configured by adding `{}` immediately after the language selection of the markdown code block.
+
+{{< highlight md >}}  
+```foo{}
+
+```
+{{< /highlight >}}
+
+---
+
+## Just line numbers
+
+`{}`
+
+{{< highlight md >}}  
+```go{}
+package main
+import "fmt"
+func main() {
+    fmt.Println("Hello world!")
+}
+```
+{{< /highlight >}}
+   
+```go{}
+package main
+import "fmt"
+func main() {
+    fmt.Println("Hello world!")
+}
+```
+
+---
+
+## Highlight specific lines
+
+`{<line numbers separated by comma>}`
+
+{{< highlight md >}}
+```go{1,3-5}
+package main
+import "fmt"
+func main() {
+    fmt.Println("Hello world!")
+}
+```
+{{< /highlight >}}
+```go{1,3-5}
+package main
+import "fmt"
+func main() {
+    fmt.Println("Hello world!")
+}
+```
+
+---
+
+## Multi step highlight
+
+`{<line numbers separated by pipe>}`
+
+{{< highlight md >}}
+```go{1|2|3-5}
+package main
+import "fmt"
+func main() {
+    fmt.Println("Hello world!")
+}
+```
+{{< /highlight >}}
+
+```go{1|2|3-5}
+package main
+import "fmt"
+func main() {
+    fmt.Println("Hello world!")
+}
+```
+---
+
+## Hiding the line numbers
+
+There is no Reveal.js parameter to use line highlighting *without* line numbers. 
+However it can be achieved by adding the some [custom CSS](https://github.com/dzello/reveal-hugo#adding-html-to-the-layout).
+
+{{< highlight html "style=github" >}}
+<style>
+  .hljs-ln-numbers {
+    display: none;
+  }
+</style>
+{{< /highlight >}}
+
+<small>💡 Tip: To hide line numbers for every presentation, put it here:</small>
+
+```text
+layouts/partials/reveal-hugo/body.html
+```