message: Prettify CHANGELOG
diff: - Rename `Slice` to `Region` to simplify differentiation between Wasm memory
  region and serde's `from_slice`
  -- Rename `Params` to `Env`, `mock_params` to `mock_env` for clearer naming
  - (this is information on the execution environment)
  +- Rename `Params` to `Env`, `mock_params` to `mock_env` for clearer naming (this
  + is information on the execution environment)
  **cosmwasm_vm**
  