feature: add support for GLFM math blocks (#987)

* feature: add support for GLFM math blocks

This add supports for GLFM's math blocks [1] using hugo's Markdown
render hooks [2].

[1]: https://docs.gitlab.com/ee/user/markdown.html#math
[2]: https://gohugo.io/templates/render-hooks/#render-hooks-for-code-blocks

Signed-off-by: Stephan Lachnit <stephanlachnit@debian.org>

layouts/_default/_markup/render-codeblock-math.html

@@ -0,0 +1,16 @@
+{{/* set default delimiters */}}
+{{ $delimiter_left := "$$" }}
+{{ $delimiter_right := "$$" }}
+
+{{/* override delimiters if set in config file */}}
+{{ with $.Page.Site.Params.katex.options.delimiters }}
+  {{ range first 1 ( where . "display" true ) }}
+    {{ $delimiter_left = index . "left" }}
+    {{ $delimiter_right = index . "right" }}
+  {{ end }}
+{{end}}
+
+{{/* output of equation */}}
+<p>{{ $delimiter_left }}
+{{ .Inner | safeHTML }}
+{{ $delimiter_right }}</p>

userguide/content/en/docs/adding-content/diagrams-and-formulae/index.md

@@ -29,11 +29,22 @@ The following code sample produces an introductory text line followed by a formu
 
 ```tex
 The probability of getting \\(k\\) heads when flipping \\(n\\) coins is:
-$$\tag*{(1)} P(E) = {n \choose k} p^k (1-p)^{n-k}$$
+$$
+\tag*{(1)} P(E) = {n \choose k} p^k (1-p)^{n-k}
+$$
 ```
 
 The probability of getting \\(k\\) heads when flipping \\(n\\) coins is:
-$$\tag*{(1)}  P(E) = {n \choose k} p^k (1-p)^{n-k}$$
+$$
+\tag*{(1)}  P(E) = {n \choose k} p^k (1-p)^{n-k}
+$$
+
+You can also use [GLFM's math blocks](https://docs.gitlab.com/ee/user/markdown.html#math) (requires hugo 0.93 or newer):
+````markdown
+```math
+\tag*{(1)} P(E) = {n \choose k} p^k (1-p)^{n-k}
+```
+````
 
 {{% alert title="Tip" %}}
 This [wiki page](https://en.wikibooks.org/wiki/LaTeX/Mathematics) provides in-depth information about typesetting mathematical formulae using the \\(\LaTeX\\) typesetting system.