feat: add multilingual mode support (#241)

BREAKING CHANGE:  Layout file renamed ´layouts/partials/page-footer.html → layouts/partials/menu-nextprev.html`. If you use overrides, you might need to change the filenames as well.

exampleSite/content/en/shortcodes/katex.md

@@ -0,0 +1,39 @@
+---
+title: KaTeX
+---
+
+[KaTeX](https://katex.org/) shortcode let you render math typesetting in markdown document.
+
+## Example
+
+{{< columns >}}
+
+```latex
+{{</* katex [display] [class="text-center"] */>}}
+f(x) = \int_{-\infty}^\infty\hat f(\xi)\,e^{2 \pi i \xi x}\,d\xi
+{{</* /katex */>}}
+```
+
+<--->
+
+<!-- spellchecker-disable -->
+<!-- prettier-ignore -->
+{{< katex display >}}
+f(x) = \int_{-\infty}^\infty\hat f(\xi)\,e^{2 \pi i \xi x}\,d\xi
+{{< /katex >}}
+
+<!-- spellchecker-enable -->
+
+{{< /columns >}}
+
+KaTeX can also be used inline, for example {{< katex >}}\pi(x){{< /katex >}} or used with a `display` setting. for example `display: block`:
+
+<!-- spellchecker-disable -->
+<!-- prettier-ignore -->
+{{< katex display >}}
+f(x) = \int_{-\infty}^\infty\hat f(\xi)\,e^{2 \pi i \xi x}\,d\xi
+{{< /katex >}}
+
+<!-- spellchecker-enable -->
+
+Text continues here.