PotatoHashing

Also, this LCT doesn't fix #117. It would need the changes from https://codeforces.com/blog/entry/67637 or the Chinese blog.

I forgot to push my most recent changes before making the PR. It's pushed now.

We discussed this on Discord but I should probably repeat it here. Feel free to take this over @Chillee (or anyone else interested).

I think we have a similar issue, except it just fails silently without throwing an error. See `;duel history Denjell`

Would we have to register CSES handles?