add missing documentation

src/aes.rs

@@ -62,6 +62,11 @@ impl<R: Read> AesReader<R> {
     /// password was provided.
     /// It isn't possible to check the authentication code in this step. This will be done after
     /// reading and decrypting the file.
+    ///
+    /// # Returns
+    ///
+    /// If the password verification failed `Ok(None)` will be returned to match the validate
+    /// method of ZipCryptoReader.
     pub fn validate(mut self, password: &[u8]) -> io::Result<Option<AesReaderValid<R>>> {
         let salt_length = self.aes_mode.salt_length();
         let key_length = self.aes_mode.key_length();

src/aes_ctr.rs

@@ -132,6 +132,7 @@ where
     }
 }
 
+/// This trait allows using generic AES ciphers with different key sizes.
 pub trait AesCipher {
     fn crypt_in_place(&mut self, target: &mut [u8]);
 }