feat: Table of Contents (#232)

Currently, the new table of contents is disabled by default. I will change that after several versions.

-------------

* feat: Table of Content (WIP)

* fix: set scratch inside define block

* fix(toc): darkmode text color

* feat: unify page layout, and add config to disable toc

* feat: add scroll-behavior: smooth to html

* fix: use <ol> for TOC. And Disable TOC by default for now

* refactor: use css flexbox for article page with toc

enable toc for example site

* feat(i18n): add i18n entry for "Back" and "Table of Contents"

* style: remove unused `keep-sidebar` class

* doc: add table of contents as feature

exampleSite/config.yaml

@@ -42,6 +42,7 @@ params:
 
     article:
         math: false
+        toc: true
         license:
             enabled: true
             default: Licensed under CC BY-NC-SA 4.0
@@ -145,5 +146,9 @@ related:
           weight: 200
 
 markup:
+    tableOfContents:
+        endLevel: 4
+        ordered: true
+        startLevel: 2
     highlight:
         noClasses: false