Add alternative encryption algorithms

[vitonsky]

I've opened issue #894 but it has been closed with no attention, it looks that my suspicious is justified.

What about add more secure ciphers/encryption algorithms like twofish, serpent, kuznyechik to let user choose encryption they trust?

You've mentioned that currently implemented AES and XChaCha20-Poly1305, but your answer looks like USA government approved just these 2 algorithms to use in gocryptfs because they have some backdoors there and told you "reject all issues about new ciphers, or you will be jailed" and this is why you pretend my feature request is not about new encryption algorithms, but about something else.