Add aead.rs from Fiono11-simplpedpop

This is not the correct way to do this, but let's stick with it for the moment.

src/aead.rs

@@ -41,7 +41,7 @@ use crate::context::SigningTranscript;
 
 use crate::cert::AdaptorCertPublic;
 
-fn make_aead<T, AEAD>(mut t: T) -> AEAD
+pub(crate) fn make_aead<T, AEAD>(mut t: T) -> AEAD
 where
     T: SigningTranscript,
     AEAD: KeyInit,