Function schnorrkel::errors::serde_error_from_signature_error

pub fn serde_error_from_signature_error<E>(err: SignatureError) -> E where
    E: Error, 

Convert SignatureError into ::serde::de::Error aka SerdeError

We should do this with From but right now the orphan rules prohibit impl From<SignatureError> for E where E: ::serde::de::Error.