[release] Release 0.2.1

CHANGES.md

-# Unreleased
+ ## Unreleased
 
-- Add `--define` (or `--def`) to define the value of a declared constant from
+- Add --define (or --def) to define the value of a declared constant from
   the command line.
 
+# 0.2.1 (19-09-2023)
+
+- [packaging] Simplify CAISAR packaging structure by merging onnx, ovo, csv and
+  onnx libraries into the main repo.
+
 # 0.2 (19-06-2023)
 
 - [prover] Integration of the [nnenum](https://github.com/stanleybak/nnenum)