* 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>
