Update changelog

CHANGES.md

@@ -1,11 +1,22 @@
+## unreleased
+
+### Deprecate
+
+- `json` types are deprecated in favor of their new `t` aliases, ahead of their removal in the next
+  major release (#73, @Leonidas-from-XIV)
+
+### Add
+
+- Add a type `t` and monomorphic `equal`, `pp` and `show` (#73, @Leonidas-from-XIV)
+
 ## 1.5.0
 
-### Changes
+### Change
 
 - Use dune as a build system (#67, @Leonidas-from-XIV)
 - reraise exceptions in `finish_string` instead of silencing them by raising a `Failure _`
 - raise finalizer exceptions in `from_channel` and `from_lexbuf` readers
 
-### Fixes
+### Fix
 
 - Fix a race condition in builds (#57, @avsm)