Rename Signature::verify to Signature::verify_document
Currently, Signature::verify
seems to be the most convenient and general operation, but it is not: it checks that the type is binary or text, unlike Signature::verify_signature
which does not. Additionally, despite its short name and apparent generality, it is a rather low-level interface, and most users don't need to use it explicitly.
Rename Signature::verify
to Signature::verify_document
(or something along those lines) to reduce confusion.