Bug fixes and improvements (#1205)

* 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

docs/chapter_searching/index.md

@@ -1,11 +1,7 @@
 # 搜索
 
-<div class="center-table" markdown>
-
 ![搜索](../assets/covers/chapter_searching.jpg)
 
-</div>
-
 !!! abstract
 
     搜索是一场未知的冒险，我们或许需要走遍神秘空间的每个角落，又或许可以快速锁定目标。