[update] Applied the updated contents of the original to the Japanese version.

[ShiMeiWo]

• Updated /lang/ja/ja.json.
• Regenerated from all .md files under the /lang/ja/ directory into HTML format.
• learn/input.md
  • Caught up the translations on the original.
  • Changed the wording of the sentence in # 4-1 to a phrase that is easier to understand as Japanese.
  • Original:

    • For convenience, contro can be used to attempt to check the input states of contros[0] and won't throw errors if a controller isn't connected yet.

  • Into:

    • For convenience, contro is provided as a shortcut accessor. It can get the input of contros[0] and will not throw any exceptions even if no game controller is connected.

• learn/world.md
  • Added two paragraphs to catch up the translations on the original.