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

README.md

@@ -27,6 +27,7 @@ Stack is a simple card-style Hugo theme designed for bloggers, some of its featu
 - No CSS framework, keep it simple and minimal
 - Properly cropped thumbnails
 - Subsection support
+- Table of contents
 
 ## Requirements