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/cpp/chapter_hashing/hash_map.cpp

@@ -0,0 +1,46 @@
+/**
+ * File: hash_map.cpp
+ * Created Time: 2022-12-14
+ * Author: msk397 (machangxinq@gmail.com)
+ */
+
+#include "../utils/common.hpp"
+
+/* ドライバーコード */
+int main() {
+    /* ハッシュテーブルを初期化 */
+    unordered_map<int, string> map;
+
+    /* 追加操作 */
+    // キー値ペア(key, value)をハッシュテーブルに追加
+    map[12836] = "Ha";
+    map[15937] = "Luo";
+    map[16750] = "Suan";
+    map[13276] = "Fa";
+    map[10583] = "Ya";
+    cout << "\nAfter adding, the hash table is\nKey -> Value" << endl;
+    printHashMap(map);
+
+    /* クエリ操作 */
+    // ハッシュテーブルにキーを入力、値を取得
+    string name = map[15937];
+    cout << "\nEnter student ID 15937, found name " << name << endl;
+
+    /* 削除操作 */
+    // ハッシュテーブルからキー値ペア(key, value)を削除
+    map.erase(10583);
+    cout << "\nAfter removing 10583, the hash table is\nKey -> Value" << endl;
+    printHashMap(map);
+
+    /* ハッシュテーブルを走査 */
+    cout << "\nTraverse key-value pairs Key->Value" << endl;
+    for (auto kv : map) {
+        cout << kv.first << " -> " << kv.second << endl;
+    }
+    cout << "\nIterate through Key->Value using an iterator" << endl;
+    for (auto iter = map.begin(); iter != map.end(); iter++) {
+        cout << iter->first << "->" << iter->second << endl;
+    }
+
+    return 0;
+}