* Add Ruby code blocks to documents
* Remove Ruby code from en/docs
* Remove "center-table" class in index.md
* Add "data-toc-label" to handle the latex heading during the build process
* Use normal JD link instead.
* Bug fixes
* Update avl_tree.md
* Remove the empty space
* Simplify the heading of the paperbook chapter
* Update hash_map_open_addressing.go to the latest version
* Improvements
* Use Roboto mono as the font of the footers
* Bug fixes
* Add the introduction to the paper book.
* Add the 'new' label to the toc
* Turn off the autoplay
* Polish the intro to paperbook