feat: Move prftree into ciphers crate

- Use a new nomenclature for these functions based on the idea of a hash
  domain (as in domain separation); this makes much more sence
- Remove the ciphers::hash export; we did not even export a hash
  function in the purest sence of the word. This gets us around the
  difficulty of figuring out what we should call the underlying
  primitive

ciphers/src/lib.rs

@@ -5,7 +5,7 @@ pub mod subtle;
 pub const KEY_LEN: usize = 32;
 const_assert!(KEY_LEN == aead::KEY_LEN);
 const_assert!(KEY_LEN == xaead::KEY_LEN);
-const_assert!(KEY_LEN == hash::KEY_LEN);
+const_assert!(KEY_LEN == hash_domain::KEY_LEN);
 
 /// Authenticated encryption with associated data
 pub mod aead {
@@ -21,8 +21,4 @@ pub mod xaead {
     };
 }
 
-pub mod hash {
-    pub use crate::subtle::incorrect_hmac_blake2b::{
-        hash, KEY_LEN, KEY_MAX, KEY_MIN, OUT_MAX, OUT_MIN,
-    };
-}
+pub mod hash_domain;