Many bug fixes and improvements (#1270)

* Add Ruby and Kotlin icons
Add the avatar of @curtishd

* Update README

* Synchronize zh-hant and zh versions.

* Translate the pythontutor blocks to traditional Chinese

* Fix en/mkdocs.yml

* Update the landing page of the en version.

* Fix the Dockerfile

* Refine the en landingpage

* Fix en landing page

* Reset the README.md

zh-hant/codes/cpp/chapter_tree/avl_tree.cpp

@@ -8,8 +8,6 @@
 
 /* AVL 樹 */
 class AVLTree {
-  public:
-    TreeNode *root; // 根節點
   private:
     /* 更新節點高度 */
     void updateHeight(TreeNode *node) {
@@ -134,6 +132,8 @@ class AVLTree {
     }
 
   public:
+    TreeNode *root; // 根節點
+
     /* 獲取節點高度 */
     int height(TreeNode *node) {
         // 空節點高度為 -1 ，葉節點高度為 0