[Userscript] Wanikani Heatmap

[Kumirei]

To transfer reviews you can follow these steps

1. Find the browser console (F12 → Console)
2. Export review cache to a string by inputting JSON.stringify(await review_cache.get_reviews())
   a. Copy the string, including enclosing quotes (just hit copy)
3. Transfer to new device by your preferred method
4. Insert into review cache review_cache.insert(JSON.parse(<string>))