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/simple_hash.cpp

@@ -0,0 +1,66 @@
+/**
+ * File: simple_hash.cpp
+ * Created Time: 2023-06-21
+ * Author: krahets (krahets@163.com)
+ */
+
+#include "../utils/common.hpp"
+
+/* 加算ハッシュ */
+int addHash(string key) {
+    long long hash = 0;
+    const int MODULUS = 1000000007;
+    for (unsigned char c : key) {
+        hash = (hash + (int)c) % MODULUS;
+    }
+    return (int)hash;
+}
+
+/* 乗算ハッシュ */
+int mulHash(string key) {
+    long long hash = 0;
+    const int MODULUS = 1000000007;
+    for (unsigned char c : key) {
+        hash = (31 * hash + (int)c) % MODULUS;
+    }
+    return (int)hash;
+}
+
+/* XORハッシュ */
+int xorHash(string key) {
+    int hash = 0;
+    const int MODULUS = 1000000007;
+    for (unsigned char c : key) {
+        hash ^= (int)c;
+    }
+    return hash & MODULUS;
+}
+
+/* 回転ハッシュ */
+int rotHash(string key) {
+    long long hash = 0;
+    const int MODULUS = 1000000007;
+    for (unsigned char c : key) {
+        hash = ((hash << 4) ^ (hash >> 28) ^ (int)c) % MODULUS;
+    }
+    return (int)hash;
+}
+
+/* ドライバーコード */
+int main() {
+    string key = "Hello algorithm";
+
+    int hash = addHash(key);
+    cout << "Additive hash value is " << hash << endl;
+
+    hash = mulHash(key);
+    cout << "Multiplicative hash value is " << hash << endl;
+
+    hash = xorHash(key);
+    cout << "XOR hash value is " << hash << endl;
+
+    hash = rotHash(key);
+    cout << "Rotational hash value is " << hash << endl;
+
+    return 0;
+}