k12: add Kt256; rename KangarooTwelve to Kt128 (#756)

This implement KT256 as specified in RFC 9861:

https://www.rfc-editor.org/rfc/rfc9861.html

Also, rename existing types `KangarooTwelve*` to `Kt128*` (e.g.
`KangarooTwelveReader` to `Kt128Reader`). This is because the
KangarooTwelve instance is specified as the KT128 instance in RFC
9861.[1]

NOTE:  For compatibility reasons, the existing types are defined as
deprecated aliases for `Kt128*`.

[1]: https://www.rfc-editor.org/rfc/rfc9861.html#section-1-3

Author: sorairolake

k12/benches/mod.rs

@@ -5,10 +5,19 @@ use digest::bench_update;
 use test::Bencher;
 
 bench_update!(
-    k12::KangarooTwelve::default();
-    k12_10 10;
-    k12_100 100;
+    k12::Kt128::default();
+    kt128_10 10;
+    kt128_100 100;
     // the bigger sizes result in OOM
-    // k12_1000 1000;
-    // k12_10000 10000;
+    // kt128_1000 1000;
+    // kt128_10000 10000;
+);
+
+bench_update!(
+    k12::Kt256::default();
+    kt256_10 10;
+    kt256_100 100;
+    // the bigger sizes result in OOM
+    // kt256_1000 1000;
+    // kt256_10000 10000;
 );