Manual fixes and a copyright note

[fscoto]

I cleaned out some leftover lint from the documentation overhaul; details in the respective commit messages.

The \& in crypto_eddsa_sign.3monocypher because Rs gets parsed as a non-existent macro otherwise and thus removed out of existence

@LoupVaillant crypto_ed25519_sign.3monocypher needs your copyright after merging because you copied the UB caveat everywhere

[LoupVaillant]

Thank you, I completely forgot about the linter & the makefile.