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_introduction/index.md

@@ -1,11 +1,7 @@
 # 初识算法
 
-<div class="center-table" markdown>
-
 ![初识算法](../assets/covers/chapter_introduction.jpg)
 
-</div>
-
 !!! abstract
 
     一位少女翩翩起舞，与数据交织在一起，裙摆上飘扬着算法的旋律。