docs: add Japanese translate documents (#1812)

* docs: add Japanese documents (`ja/docs`)

* docs: add Japanese documents (`ja/codes`)

* docs: add Japanese documents

* Remove pythontutor blocks in ja/

* Add an empty at the end of each markdown file.

* Add the missing figures (use the English version temporarily).

* Add index.md for Japanese version.

* Add index.html for Japanese version.

* Add missing index.assets

* Fix backtracking_algorithm.md for Japanese version.

* Add avatar_eltociear.jpg. Fix image links on the Japanese landing page.

* Add the Japanese banner.

---------

Co-authored-by: krahets <krahets@163.com>

ja/codes/java/chapter_tree/binary_tree.java

@@ -0,0 +1,40 @@
+/**
+ * File: binary_tree.java
+ * Created Time: 2022-11-25
+ * Author: krahets (krahets@163.com)
+ */
+
+package chapter_tree;
+
+import utils.*;
+
+public class binary_tree {
+    public static void main(String[] args) {
+        /* 二分木を初期化 */
+        // ノードを初期化
+        TreeNode n1 = new TreeNode(1);
+        TreeNode n2 = new TreeNode(2);
+        TreeNode n3 = new TreeNode(3);
+        TreeNode n4 = new TreeNode(4);
+        TreeNode n5 = new TreeNode(5);
+        // ノードの参照（ポインタ）を構築
+        n1.left = n2;
+        n1.right = n3;
+        n2.left = n4;
+        n2.right = n5;
+        System.out.println("\n二分木を初期化\n");
+        PrintUtil.printTree(n1);
+
+        /* ノードの挿入と削除 */
+        TreeNode P = new TreeNode(0);
+        // ノード P を n1 -> n2 の間に挿入
+        n1.left = P;
+        P.left = n2;
+        System.out.println("\nノード P を挿入後\n");
+        PrintUtil.printTree(n1);
+        // ノード P を削除
+        n1.left = n2;
+        System.out.println("\nノード P を削除後\n");
+        PrintUtil.printTree(n1);
+    }
+}